The Wealth Delta Tax: UK Jurisdiction and Data Reference Paper
Wealth Delta Tax, United Kingdom, UK tax system, UK public finance, UK wealth distribution, Wealth and Assets Survey, HM Treasury, OBR fiscal data, tax administration, institutional capacity, tax expenditure, national accounts, fiscal benchmarking, administrative data
Revision History
| Revision | Date | Details |
|---|---|---|
| 0.01 | 15 June 2026 | First Draft |
| 1.00 | 15 August 2026 | Published to website |
Abstract
This paper serves two purposes. The first is to justify the choice of the United Kingdom as the reference jurisdiction for the Wealth Delta Tax project and to specify what is and is not being modelled. The second is to compile the empirical data the companion papers require: the UK’s fiscal institutions, their capacities, their current functions, and the wealth and population data against which the WDT’s mechanisms will be tested.
The paper does not design or modify the WDT. It does not perform revenue calculations or model behavioural responses. Those tasks belong to other papers in the research agenda. What this paper does is establish the factual foundation those papers will build on.
A note on scope: the WDT companion papers do not model the UK as a real jurisdiction in its full constitutional, political, and legal complexity. They model an idealised country that inherits specific features from the UK, principally its population data, wealth distribution data, tax revenue data, and its basic institutional architecture. This paper makes that choice explicit, explains what is taken from the UK and why, and flags where UK-specific complications have been set aside for tractability.
Glossary
Automated valuation model (AVM): A statistical model that generates property valuations using comparable sales data, land registry records, and other observable inputs, without requiring individual professional appraisal. The VOA uses AVMs for standard residential properties.
Common Reporting Standard (CRS): The OECD framework for automatic exchange of financial account information between participating jurisdictions. CRS continues to apply to the UK post-Brexit and covers the majority of offshore financial account information relevant to WDT compliance.
DAC (Directive on Administrative Cooperation): The EU framework for automatic exchange of tax information among member states, providing broader asset-class coverage than CRS alone. The UK lost access to DAC on leaving the EU, with residual gaps concentrated in EU-domiciled holding structures.
Exemption threshold: The net worth level below which no WDT liability arises. Set high enough to exclude the substantial majority of UK households; a design variable rather than a design principle. See (WP §3.3).
First-tier Tribunal (Tax Chamber): The initial appellate body for disputes between HMRC and taxpayers across all UK tax types. Relevant to WDT as the venue for contested valuation disputes and the Route D auction process.
HMRC (His Majesty’s Revenue and Customs): The UK’s primary tax collection authority and the assumed administrative home for WDT operations in the UK reference jurisdiction.
IFS (Institute for Fiscal Studies): Independent UK economic research body. The IFS, through Advani et al. (2020) and related work, provides the principal supplementary estimates of UK wealth concentration used where WAS data is inadequate.
Labour tax relief dividend: The progressive reduction in taxes on wages and consumption that WDT revenue is intended to finance. The mechanism through which the WDT’s terminal goal is actually pursued. See (WP §6).
OBR (Office for Budget Responsibility): The UK’s independent fiscal watchdog, established in 2010 and placed on a statutory footing in 2011. Provides the primary institutional precedent for the WDT’s Sovereign Wealth Fund Custodian role in the UK reference jurisdiction.
Reference jurisdiction: A specific country selected to ground the WDT’s companion papers in concrete institutional data, population figures, and legal context. The reference jurisdiction does not constrain the whitepaper’s generic mechanism design.
SWF Custodian: The body responsible for managing the Sovereign Wealth Fund and ensuring the refund liability remains pre-funded. In the UK reference jurisdiction, maps to the Bank of England or a dedicated statutory body modelled on the Bank’s independence architecture. See (GOV.B §E.6).
Tax gap: The difference between the theoretical tax liability in the UK and the amount actually collected. Stood at £46.8 billion (5.3%) in 2023-24. The WDT primarily addresses the portion attributable to wealthy individuals.
Upper Tribunal (Tax and Chancery Chamber): The appellate body hearing points of law from the First-tier Tax Chamber. The second tier of the UK’s tax dispute system.
Valuation Office Agency (VOA): An executive agency of HMRC responsible for property valuations underpinning business rates and council tax across England and Wales. Provides the institutional starting point for WDT property valuation in the UK reference jurisdiction.
Valuation Tribunal Service (VTS): The independent tribunal handling appeals against VOA business rate and council tax valuations. Relevant as a cost baseline for specialist valuation appeal bodies.
WAS (Wealth and Assets Survey): The ONS longitudinal survey providing the primary UK household wealth dataset. Lost Official Statistics accreditation in June 2025; treated as indicative background only, supplemented by HMRC administrative data and Advani et al. (2020) IFS estimates.
Wealth Tax Commission: The body that produced Advani et al. (2020), the most directly comparable prior UK wealth tax proposal to the WDT. Recommended a one-off wealth tax rather than an annual charge, primarily on administrative grounds.
1. The UK as Reference Jurisdiction
1.1 Why a Reference Jurisdiction at All
The WDT whitepaper is deliberately generic, which is right for mechanism design. The companion papers reach points where abstract treatment fails: governance architecture needs an account of what entrenchment means in a specific constitutional context; revenue modelling needs actual wealth distribution data; valuation infrastructure design needs engagement with existing institutions.
A reference jurisdiction grounds the companion papers without constraining the whitepaper. Without one, (RATES) revenue modelling and the behavioural response work in (WP §9.1) remain notional; with one, they become concrete tasks with defined data sources.
1.2 Why the UK
The UK scores well across the relevant criteria and is substantially more useful than any comparable candidate.
1.2.1 Wealth Data
The WAS, run by the ONS, provides longitudinal household wealth data decomposed by asset class. It oversamples the top wealth percentile by a factor of five. The top 10% holds approximately half of all surveyed wealth; the IFS estimates the top 1% holds around 23%, above the WAS headline of 18%, reflecting known survey limitations at the top of the distribution.
Caveat: the Office for Statistics Regulation removed Official Statistics accreditation from WAS in June 2025, citing quality concerns since COVID-19 disrupted fieldwork. WAS is treated as indicative background only; primary reliance falls on HMRC administrative data and Advani et al. (2020) IFS estimates; revenue projections should carry wider confidence intervals than Advani et al. (2020) used, given WAS degradation and the absence of a formal HMRC data access arrangement.
1.2.2 Administrative Capacity
HMRC is a large, technically capable revenue authority with demonstrated experience on complex instruments. This matters because the WDT’s design claim is that its administrative demands are not extraordinary relative to what developed tax authorities already do; the UK tests that claim. The VOA, as an HMRC executive agency, provides property valuations at national scale and offers a direct precedent for the statutory valuation function the WDT requires.
1.2.3 Constitutional Flexibility
Parliament is sovereign; the UK has no written constitution. This makes the WDT’s entrenchment question a design problem rather than a legal barrier. The OBR model, established in 2010 and on a statutory footing by 2011, shows that durable independent fiscal institutions can be created through ordinary legislation.
1.2.4 Political Salience
Wealth taxation has been an active part of UK political debate since 2019. Advani et al. (2020) produced a directly comparable proposal through the Wealth Tax Commission. The LSE, Resolution Foundation, and IFS have all published relevant work on UK wealth distribution and taxation. The intellectual infrastructure for this project exists in the UK in a way it does not in most comparable jurisdictions.
1.2.5 Researcher Familiarity
The author is a UK native. Institutional knowledge that cannot be acquired through reading official documents (how HMRC operates under administrative pressure, what the OBR’s independence has meant in practice, what the realistic political economy of fiscal reform looks like) improves the analysis. This is a practical consideration, not a trivial one.
1.3 What Is and Is Not Being Modelled
The companion papers model an idealised country that takes specific features from the UK, not the UK as a real political and legal system. Modelling the latter would make the project unmanageable and produce a paper about UK-specific complications rather than the WDT’s mechanisms.
What the idealised country inherits: population and demographic data (approximately 69 million people, the UK household count, GDP, and wealth distribution from WAS and supplementary sources); tax revenue data (UK headline revenues with the same broad composition across income tax, National Insurance, VAT, and corporation tax); and institutional architecture in outline (a competent tax authority on the HMRC model, an independent fiscal institution on the OBR model, a statutory valuation body on the VOA model, and a specialist tax tribunal system, all assumed functional).
What is not modelled: parliamentary sovereignty as the specific entrenchment mechanism ((GOV) uses a generic statutory entrenchment model, taking the Budget Responsibility and National Audit Act 2011 as precedent rather than constraint); post-Brexit information exchange complications (the idealised country is assumed to participate fully in standard international exchange frameworks); devolution (the idealised country is a unitary state); and the UK’s non-dom regime, which provides useful behavioural evidence but is not a structural feature of the idealised country.
1.4 The Wealth Tax Commission Comparison
Advani et al. (2020), produced by the Wealth Tax Commission with access to HMRC administrative data, is the most directly comparable prior UK proposal to the WDT. It provides a detailed evidence base on wealth distribution, revenue potential, and administrative costs.
The WTC recommended a one-off charge rather than an annual tax: £500,000 threshold per individual, 1% per year over five years, raising an estimated £260 billion. It concluded that annual wealth taxation would be substantially harder to administer than a one-off charge, primarily because of the recurring valuation problem.
The WDT taxes the annual change in net worth rather than the stock, which reduces but does not eliminate the recurring valuation burden. It includes a symmetric loss-refund mechanism the WTC proposal lacks, operates at a high threshold targeting a small population rather than the broad £500,000 WTC base, and has a cooperative institutional architecture that differs materially from a standard wealth tax. The WTC’s administrative conclusion is well-founded; the valuation paper’s framework is partly a response to it.
Where Advani et al. (2020) data and analysis remain useful, this paper draws on them. Their revenue modelling, threshold sensitivity analysis, and administrative cost evidence are the most directly relevant prior work for the microsimulation agenda in (WP §9.1).
1.5 UK Institutional Architecture and WDT Requirements
This section maps the WDT’s principal institutional requirements against the UK institutions that would carry them, identifying where existing capacity is adequate, where expansion is needed, and where new functions must be built.
1.5.1 HMRC
HMRC is the primary administrative body for UK taxation and the natural home for WDT administration.
Current capacity: approximately 63,600 FTE as of 2023-24 (down from 63,738 in 2022-23), with a departmental expenditure limit of £6.8 billion in 2025-26. HMRC collected approximately £829 billion in 2024-25. The tax gap stood at 5.3% (£46.8 billion) in 2023-24. HMRC handles 88.5 million app logins annually from 3.8 million unique users.
WDT requirements: annual net worth reporting for a small population, probably 20,000 to 50,000 individuals at a high threshold (Advani et al., 2020). This is small relative to HMRC’s self-assessment population of several million. The principal new demands are integration with existing self-assessment infrastructure; oversight of valuation submissions; administration of the refund mechanism; and cross-checking declarations against land registry, company filings, and financial institution data.
The core task is within HMRC’s existing capabilities. The IR35 and loan charge episodes show that HMRC can fail on complex new instruments when rollout is rushed or underfunded, which is an argument for the phased implementation pathway in WP rather than a fundamental capacity objection. The specific challenge is building the data infrastructure for annual net worth tracking, which does not exist in integrated form.
1.5.2 The Valuation Office Agency
The VOA is an HMRC executive agency providing property valuations for business rates and council tax in England and Wales, underpinning approximately £62 billion in annual local taxation revenue. It employs approximately 3,830 people across 35 locations and maintains around 2.1 million non-domestic and 26 million council tax properties. It uses automated valuation models for standard properties and professional surveyors for complex cases.
Current capacity: the VOA employs approximately 3,830 people across 35 locations and maintains valuations for around 2.1 million non-domestic properties and 26 million council tax properties in England and Wales. Its existing system combines automated valuation models for standardised properties with professional surveyor judgement for more complex or atypical cases. The VOA therefore already operates a national-scale property valuation function with statutory procedures for valuation challenges and appeals, supporting approximately £62 billion in annual local taxation revenue.
WDT requirements: the WDT needs a valuation function for illiquid assets held by a small wealthy population. For residential and commercial property, this overlaps significantly with what the VOA already does; for private company equity, the VOA has no current function and a new certified valuation profession under the WDT Valuation Code would be required. The VOA’s statutory framework, automated modelling, and appeal mechanisms provide a design template even where the WDT needs capacity the VOA does not have.
As (JUR §1.5.2) establishes, the VOA’s existing capacity is adequate for WDT property valuations once the route architecture in (VAL §4) is applied: its role is confined to automated valuation of standard property, which it already performs at national scale. For private company equity and complex financial assets, new capacity is needed. The governance framework for extending professional valuation oversight to the WDT context is provided by the Pereira Gray (2021) review, accepted by RICS in 2022; mandatory rotation requirements (RICS, May 2024) and independent quality assurance panels are directly relevant design elements.
1.5.3 The Office for Budget Responsibility
The OBR is the UK’s independent fiscal watchdog, established in 2010 and placed on a statutory footing by the Budget Responsibility and National Audit Act 2011. It produces independent economic and fiscal forecasts, scrutinises government performance against fiscal rules, and publishes long-run fiscal sustainability analysis.
Current capacity: 52 permanent civil servants and a three-member Budget Responsibility Committee whose appointments the Treasury Select Committee can veto. Its budget sits within the Treasury’s spending review allocation, creating a limitation on its formal independence. The OBR has nevertheless maintained operational independence since establishment. The chair’s resignation in December 2025 following an accidental early release of forecast data was a significant reputational episode worth noting. The Resolution Foundation’s February 2026 assessment found that the OBR broadly performs its statutory functions well but is under-resourced relative to comparable international institutions, noting that it has roughly half the staff of the Netherlands’ CPB and around a third of Belgium’s Federal Planning Bureau despite operating in a substantially larger economy.
WDT requirements: (GOV §6.3) identifies the SWF Custodian as the WDT’s mandate guardian. Its function is not to administer the tax, value assets, produce economic forecasts, or set the inputs against which its own performance is scored. It requires statutory independence; long, overlapping, non-renewable tenure; stewardship statements creating a ratcheting reputational commitment; outputs preserved in the permanent public record; and no role in setting the conditions or performance measures against which its stewardship is assessed. Its operational task is therefore relatively small in administrative terms but institutionally demanding: it must maintain sufficient expert capacity to monitor compliance with the SWF mandate, assess whether drawdown conditions have been met, publish independent stewardship assessments, and provide a durable institutional check against political drift.
The OBR model — a small expert body with statutory independence and TSC oversight of appointments — is the most directly relevant UK precedent. In the UK reference jurisdiction, the Custodian maps to the Bank of England or to a dedicated statutory body constructed on the Bank’s independence architecture (GOV.B §E.6). The OBR demonstrates that parliamentary sovereignty does not prevent the creation of durable independent fiscal institutions. The design elements that have held are the statutory mandate, TSC veto over appointments, and transparency obligations. The budget allocation weakness is real but has not, to date, compromised independence in practice.
The Resolution Foundation’s February 2026 assessment is particularly relevant to the WDT design because it demonstrates that formal independence alone does not guarantee adequate institutional capacity. The OBR’s comparatively small staffing level and dependence on the Treasury spending review allocation create vulnerabilities that the Custodian should not inherit. This informed the design in (GOV §6.3): the Custodian’s budget should not be subject to the same vulnerability, while the three anti-drift requirements—pre-crisis public commitment to drawdown conditions, overlapping long non-renewable tenure, and periodic stewardship statements—create protections extending beyond the OBR model.
Whether the actual OBR fully meets the structural standard specified in (GOV §6.3), particularly when tested against the 2022 mini-budget period and the December 2025 resignation, is assigned to Phase One at (JUR §4.2). The WDT does not depend on assuming that the existing OBR itself is the appropriate Custodian. Rather, the OBR provides evidence that a small, expert, statutory institution can maintain meaningful independence within the UK’s constitutional framework, while its identified weaknesses provide direct design lessons for the stronger independence architecture required by the WDT Custodian.
1.5.4 The Tax Tribunal System
The UK tax dispute system runs through the First-tier Tribunal (Tax Chamber) and the Upper Tribunal (Tax and Chancery Chamber); the First-tier handles initial appeals and the Upper Tribunal hears points of law from it.
Current capacity: overall tribunal open caseloads reached approximately 795,000 by end September 2025, an 18% annual increase. The First-tier Tax Chamber saw increased receipts from 2023-24. The system is primarily staffed by fee-paid part-time judges drawn from the legal profession.
WDT requirements: the valuation paper’s two-stage review process and the Route D auction mechanism both require tribunal oversight for contested cases. Given the small WDT taxpayer population, dispute volume would be manageable relative to the overall caseload. The concern is expertise: WDT valuation disputes involving private company equity require financial and accounting competence, not only legal expertise. The Special Commissioners, predecessors to the current chamber, had this; the current chamber has it to a degree, but complex valuation cases are among the most resource-intensive.
The existing tribunal architecture is adequate in principle. The practical problem is backlog and capacity pressure: adding technically complex valuation disputes to an already-stretched system requires careful management, and the phased implementation pathway in WP is the right response. A small early WDT population would generate a manageable volume of test cases before the system scales.
2. Data Reference
This section compiles the key data the companion papers will draw on. All figures are from publicly available official statistics unless otherwise noted. Data gaps are flagged explicitly.
2.1 Population and Economy
| Indicator | Value | Source |
|---|---|---|
| UK population (2024) | 69.2 million | ONS / World Bank |
| UK households (approx). | 28 million | ONS |
| UK GDP (2024, nominal) | £2.65 trillion approx. | ONS |
| UK GDP per capita (2025) | £40,591 (approx. $53,246 USD) | Statista / World Bank |
| GDP growth (2024) | 1.1% | ONS |
| UK government spending (2024-25) | £1.29 trillion | HMT / Statista |
| Government spending as % of GDP | approx. 44–45% | OBR |
| UK deficit (2023-24) | £131 billion | HMT |
| UK public debt (end 2024-25) | approx. £2.8 trillion (93.2% GDP) | ONS |
2.2 Tax Revenues
Total HMRC tax receipts 2024-25: approximately £829 billion. The breakdown covers the main heads relevant to the WDT’s long-run objective of reducing the burden on labour income.
| Tax Head | 2023-24 Receipts | Notes |
|---|---|---|
| Income tax | £273.3 billion | 10% increase on prior year, partly driven by frozen thresholds |
| National Insurance contributions | £177.7 billion | Slight increase despite rate reduction |
| VAT | £168.9 billion (approx). | Largest indirect tax |
| Corporation tax | Approx. £88 billion | Increased in recent years |
| Capital gains tax | Approx. £14–16 billion | Volatile, concentrated at top |
| Inheritance tax | £7.5 billion | Growing due to frozen thresholds |
| Total HMRC receipts (2023-24) | £827.7 billion | Record level, 5% increase on prior year |
| Total HMRC receipts (2024-25) | Approx. £829 billion | Continued growth |
The tax gap was 5.3% (£46.8 billion) in 2023-24. Approximately one third is attributable to small businesses; a smaller share to wealthy individuals, the WDT’s primary target.
2.3 Government Expenditure Breakdown
| Department / Function | Spend 2023-24 | % of total |
|---|---|---|
| Social protection (DWP) | £275.1 billion | 26% |
| Health and Social Care | £196.7 billion | 19% |
| Education | £127.0 billion (approx). | 12% |
| Treasury (debt interest etc). | Approx. £100 billion | 8–9% |
| Defence | £57.6 billion | 5% |
| Transport | £32.6 billion | 3% |
| Total government expenditure | £1,189 billion | 100% |
Health spending has grown from 2.8% of GDP in 1955-56 to 8.4% in 2024, the dominant structural shift in public spending over 70 years. Social protection at approximately 10.9% of GDP is the largest single category, projected to reach £373 billion by 2029-30.
The labour tax relief dividend requires reducing income tax and National Insurance receipts. These two heads account for approximately £450 billion annually, giving substantial headroom for meaningful rate reductions even at modest WDT revenue levels.
2.4 Wealth Distribution
The primary source is the ONS WAS. As noted in (JUR §1.2.1), WAS lost Official Statistics accreditation in June 2025 and should be treated with caution. Advani et al. (2020) IFS work provides partial corrections at the top of the distribution.
| Measure | Value | Source |
|---|---|---|
| Median individual wealth (2018-20) | £125,000 | ONS WAS |
| Mean individual wealth (2018-20) | £305,000 | ONS WAS |
| Top 10% wealth share (WAS) | Approx. 50% | ONS WAS |
| Top 1% wealth share (WAS) | Approx. 18% | ONS WAS |
| Top 1% wealth share (IFS adjusted) | Approx. 23% | Advani et al. (2020) |
| Top 1% entry threshold (individual) | Approx. £3.6 million | ONS WAS 2018-20 |
| Top 1% households (approx). | 263,000 households | ONS estimate |
| Top 0.1% entry threshold (estimate) | Approx. £10 million+ | Advani et al. (2020) / IFS |
| Number of individuals with £10m+ wealth | Approx. 32,000 | Advani et al. (2020) |
The WAS oversamples the top percentile by a factor of five, but the wealthiest individuals remain underrepresented. At the WDT’s likely threshold, HMRC administrative data and company filings are more reliable than survey data.
Total household wealth in Great Britain has roughly doubled as a share of national income over 30 years. Net property wealth accounts for approximately 40% of total household wealth in 2020-22. Private pension wealth is the largest component for individuals in the upper distribution, particularly in the £500,000 to £3 million range.
2.5 HMRC Institutional Data
| Indicator | Value | Source |
|---|---|---|
| HMRC full-time equivalent staff (2023-24) | 61,186 FTE | HMRC Annual Report |
| HMRC FTE (2022-23) | 63,738 FTE | HMRC Annual Report |
| HMRC total budget (DEL, 2023-24) | £7.4 billion | HMRC / Wikipedia |
| HMRC DEL (2025-26) | £6.8 billion | Spending Review 2025 |
| Additional compliance staff being recruited (to 2029) | 5,500 | Budget 2024 / Spring Statement 2025 |
| Additional debt management staff (to 2029) | 2,400 | Budget 2024 / Spring Statement 2025 |
| Self-assessment users | Several million (exact varies by year) | HMRC |
| HMRC app unique users (2023-24) | 3.8 million | HMRC Annual Report |
| HMRC app logins (2023-24) | 88.5 million | HMRC Annual Report |
| Tax gap (2023-24) | £46.8 billion (5.3% of theoretical liability) | HMRC |
2.6 Valuation Office Agency Institutional Data
| Indicator | Value | Source |
|---|---|---|
| VOA staff (FTE, 2022-23) | Approx. 3,830 | VOA Annual Report 2022-23 |
| VOA office locations | 35 across England, Scotland, Wales | VOA Annual Report |
| Annual taxation underpinned by VOA work | £62 billion (business rates + council tax) | VOA Annual Reports |
| Non-domestic (business rate) properties on list | Approx. 2.1 million | VOA |
| Council tax properties | Approx. 26 million | VOA |
| Valuation Tribunal Service operating expenditure | £5.2 million (2024-25) | VTS Annual Report 2024-25 |
The VTS, which handles appeals against VOA council tax and business rate valuations, operates on £5.2 million with staffing at 68% of that. This is a baseline for what a small specialist valuation appeal body costs. A WDT valuation tribunal, handling a smaller but more complex caseload, would likely cost more per case but less in aggregate.
2.7 OBR Institutional Data
| Indicator | Value | Source |
|---|---|---|
| OBR permanent staff (2024-25) | 54 civil servants | OBR |
| Budget Responsibility Committee members | 3 (with TSC veto on appointments) | Budget Responsibility and National Audit Act 2011 |
| OBR established | May 2010 (statutory footing 2011) | |
| OBR budget | Within Treasury DEL (not ring-fenced) | Resolution Foundation 2026 |
| Independent fiscal institutions with wider remit | OBR is larger than most comparable IFIs per capita | Resolution Foundation 2026 |
2.8 Tax Tribunal System Data
| Indicator | Value | Source |
|---|---|---|
| Overall tribunal open caseload (end Sep 2025) | 795,000 | HMCTS Tribunal Statistics Q2 2025-26 |
| Year-on-year caseload increase | 18% in the year to Sep 2025 | HMCTS Tribunal Statistics |
| First-tier Tax Chamber receipts trend | Increasing; sharp upturn noted in 2023-24 | HMCTS Tribunal Statistics |
| Primary driver of tribunal growth | Immigration and asylum; employment; SSCS | HMCTS |
| Tax chamber as share of total caseload | Small minority; dominated by immigration, employment, SSCS | HMCTS |
The tribunal backlog is a systemic concern independent of the WDT. A WDT valuation dispute involving private company equity would sit at the complex end of the tax chamber’s caseload. Volume would be small given the high threshold, but expertise requirements would be significant.
2.9 Capital Gains Tax and Inheritance Tax: Baseline Data
CGT and IHT baseline data are relevant for revenue context and behavioural response modelling.
| Indicator | Value | Notes |
|---|---|---|
| CGT receipts (2023-24) | Approx. £14–16 billion | Volatile; concentrated in top taxpayers |
| CGT taxpayers (approx). | Approx. 350,000–400,000 | Small relative to income taxpayer population |
| IHT receipts (2023-24) | £7.5 billion | Growing due to frozen nil-rate band |
| IHT effective taxpayer estates (approx). | Approx. 4% of deaths per year | HMRC |
| Non-dom regime (pre-reform) | Approx. 68,000 non-dom taxpayers | HMRC (historic) |
CGT receipts are highly concentrated in a small number of high-value transactions. This is consistent with the WDT’s assumption that the tax base sits in a small population whose wealth changes are large enough to justify the administrative infrastructure required to measure them.
2.10 Data Gaps and Limitations
The following gaps should be addressed before the revenue microsimulation in (WP §9.1) is finalised.
Wealth data at the very top: the WAS systematically undersamples individuals above approximately £3 million. The WDT’s likely taxable population starts somewhere in the £5 million to £10 million range, where WAS provides limited direct evidence. HMRC administrative data supplemented by Advani et al. (2020) is the best available proxy. The OSR’s removal of WAS accreditation in June 2025 makes this gap explicit.
Private company ownership data: VAL requires data on the number of UK individuals holding significant private company stakes and the distribution of those values. Companies House provides registration information but not valuation. HMRC data from IHT and CGT returns offers a partial window but is not publicly available at the required granularity. This is an open data requirement for the revenue modelling agenda.
Offshore asset exposure: the extent of UK-resident wealth held offshore outside existing exchange frameworks is not precisely knowable from public data. The HMRC tax gap for wealthy individuals likely understates the true figure. Post-Brexit changes to some bilateral arrangements mean pre-2020 evidence is less directly applicable. Behavioural response modelling must handle this through scenario analysis.
VOA capacity by asset type: VOA public data does not break down by asset class in a way that maps cleanly to WDT requirements. The distinction between residential property (high volume, AVM viable), commercial property (lower volume, more specialist), and private company equity (VOA has no current function) matters significantly for VAL’s design. This gap is flagged for future research.
2.11 Model Input Data Provenance
This subsection anchors each primary data input used in the RATES and VAL models against its source. The TOML parameter file (WDT_Params.toml) is the single source of truth for all model inputs; the values below are reproduced from that file with their verified derivations. This subsection was added in v1.8 following a cross-file audit of all TOML inputs against their originating datasets.
Equity return series (returns.values, 73 annual observations, 1947–2019). Source: Jordà, Ò., Knoll, K., Kuvshinov, D., Schularick, M., & Taylor, A. M. (2019). The rate of return on everything, 1870–2015. Quarterly Journal of Economics, 134(3), 1225–1298. Data file: JSTdatasetR6.xlsx, column capital_tr, iso = GBR, calendar years 1947–2019. All 73 TOML values match the JST source to four decimal places. The series records UK equity capital total returns at annual frequency, running from −5.78% (2008) to +40.71% (1975); five negative-return years occur: 1948, 1949, 1990, 2008, and 2018. The arithmetic mean across all 73 years is 10.4529%, which rounds to the hist_mean = 10.45% used as the tier-differential baseline throughout the companion models. The geometric mean is 10.15%; the models use the arithmetic mean as the baseline, consistent with standard practice for linear return models where cross-period compounding is handled by the simulation. Note: the JST dataset also contains an eq_tr column (equity total return including dividends), which is a materially different series; the RATES model uses capital_tr (capital gains component only) throughout.
Budget base (budget_base = 1157.4, £b). Source: HM Treasury. (2024). Public Expenditure Statistical Analyses 2024 (PESA 2024), Table 10: Total expenditure on services by sub-function. Data file: PSS_May_2024_TES_UPDATED.xlsx, Table_10, row “Total Managed Expenditure”, fiscal year 2022–23 outturn = £1,157.4 billion. The value is confirmed exactly against the primary source.
Budget growth rate (budget_growth = 0.0451, 4.51% p.a.). Source: HM Treasury. (2024). Public Expenditure Statistical Analyses 2024 (PESA 2024), Table 10: Total Managed Expenditure, nominal. Data file: PSS_May_2024_TES_UPDATED.xlsx, Table_10, fiscal years 1999–00 to 2019–20. The rate is derived as the compound annual growth rate of nominal TME from £367.9 billion in 1999–00 to £888.4 billion in 2019–20 over 20 fiscal years: (888.4 / 367.9)^(1/20) − 1 = 4.5067%, rounded to 4.51%. The terminal year of 2019–20 is used deliberately: fiscal year 2020–21 (£1,107.2 billion) is excluded as a non-representative endpoint because its 24.7% single-year increase reflects COVID-19 emergency spending rather than the underlying structural expenditure trend. This replaces the prior non-reproducible derivation; the corrected 4.51% value is used in all model runs from RATES v[next] onward. The correction is conservative-weakening: the lower growth rate produces a smaller projected expenditure denominator and therefore raises RATES coverage ratios relative to the prior figures. No design position or mechanism is affected.
Wealth bracket populations and starting wealth (brackets.N_pop, brackets.V0_m). Primary source: Office for National Statistics. (2022). Wealth and Assets Survey, Wave 7: April 2018 to March 2020, Table 2.4 (household total wealth by decile, summary statistics). Supplementary source: Advani et al. (2020). The bracket populations sum to approximately 34.6 million, representing the modelled active-taxpayer population. Starting-wealth values for the top four brackets (99th percentile and above) are model-implied via Pareto extrapolation at \(\alpha\) = 2.25 and not directly observed; WAS systematically undersamples above approximately £3 million and lost ONS Official Statistics accreditation in June 2025. The caveat at (JUR §2.4) applies in full: the Pareto tail is lighter than the true distribution, and revenue projections for top-bracket taxpayers carry wider confidence intervals than the central estimates suggest.
Rate function parameters (tau_0, tau_m, k, $W_{min}$). Design parameters, not empirically derived quantities. The canonical values (\(\tau_0\) = 15%, \(\tau_m\) = 70%, \(k\) = 0.001 per £m, \[W_{min}\] = £2m) constitute the Balanced scenario used throughout (RATES). Justification and full sensitivity analysis across the parameter space are in (SWEEPS) and (SWEEPS.A).
SWF capitalisation parameters (srr_ratio = 3.0, lrr_years = 3.0). Design parameters derived from the (RATES) solvency analysis. The 3× SRR ratio is the recommended Governing Council floor: the 2007 Balanced reference scenario (worst-case starting year on the LRR fill dimension) first shows a covered SRR breach below 2.5× and no breach at 2.5× or above; 3× provides margin above that threshold. The 3-year LRR floor is discussed in (GOV.B §E.1).
3. Data Summary
3.1 UK Government Income 2024-25
| Tax Head | £bn | % of Total Receipts | % of GDP |
|---|---|---|---|
| Income Tax | 302.8 | 35.3% | 10.3% |
| National Insurance Contributions | 172.5 | 20.1% | 5.9% |
| VAT | 171.0 | 19.9% | 5.8% |
| Corporation Tax (incl. EPL, bank levies, DST) | 97.5 | 11.4% | 3.3% |
| Capital Gains Tax | 13.7 | 1.6% | 0.5% |
| Stamp Taxes (SDLT, SDRT, ATED) | 18.3 | 2.1% | 0.6% |
| Fuel Duty | 24.4 | 2.8% | 0.8% |
| Inheritance Tax | 8.3 | 1.0% | 0.3% |
| Alcohol Duty | 12.6 | 1.5% | 0.4% |
| Tobacco Duty | 7.9 | 0.9% | 0.3% |
| Air Passenger Duty | 4.1 | 0.5% | 0.1% |
| Environmental Taxes | 2.9 | 0.3% | 0.1% |
| Other / residual | 23.6 | 2.6% | 0.8% |
| Total HMRC Receipts | 858.6 | 100% | 29.3% |
| Council Tax and other local revenues | ~60 | ||
| Non-tax receipts (interest, dividends, fines) | ~50 | ||
| Total Public Sector Receipts | ~1,058 | 36.1% |
3.2 UK Government Expenditure 2024-25
| Function | £bn | % of TME | % of GDP |
|---|---|---|---|
| Social Protection (total) | 384 | 29.7% | 13.1% |
| of which: Old Age / State Pension | 162.7 | 12.6% | 5.5% |
| of which: Other welfare / DWP | 221.3 | 17.1% | 7.5% |
| Health (NHS and public health) | 242 | 18.7% | 8.2% |
| General Public Services (incl. debt interest) | 158 | 12.2% | 5.4% |
| of which: Debt interest | 84.8 | 6.6% | 2.9% |
| Education | 119 | 9.2% | 4.1% |
| Economic Affairs (incl. transport, enterprise) | 87 | 6.7% | 3.0% |
| of which: Transport | 46.4 | 3.6% | 1.6% |
| Defence | 57.6 | 4.5% | 2.0% |
| Housing and Community Amenities | 22.3 | 1.7% | 0.8% |
| Public Order and Safety | ~36 | 2.8% | 1.2% |
| Recreation, Culture and Religion | ~15 | 1.2% | 0.5% |
| Environmental Protection | ~15 | 1.2% | 0.5% |
| Total Managed Expenditure | 1,290.6 | 100% | 44.0% |
3.3 Fiscal Summary
| £bn | |
|---|---|
| Total public sector receipts | ~1,058 |
| Total managed expenditure | 1,290.6 |
| Deficit | ~232 |
| GDP (2024-25) | ~2,932 |
| Public debt (end 2024-25) | ~2,800 (93.2% GDP) |
4. Limitations and Further Work
4.1 Formal modelling gaps
No items in this paper.
4.2 Phase One empirical unknowns
Whether the actual OBR meets the structural properties requires of the SWF Custodian — statutory independence, long overlapping non-renewable tenure, stewardship statements creating a ratcheting reputational commitment, no role in setting the inputs against which its performance is scored — requires empirical assessment of specific episodes unavailable at the design stage. (GOV §6.3) resolves the structural question; the empirical mapping is assigned to Phase One.
4.3 Jurisdiction-specific legal and implementation work
HMRC data access. A formal HMRC data access arrangement requires institutional affiliation or partnership with an established research body. It is a precondition for revenue microsimulation rather than a Phase One output; until it exists, revenue projections rely on publicly available statistics with acknowledged data limitations.
Post-Brexit information exchange. The UK’s loss of DAC access and EU beneficial ownership register interconnection leaves a residual gap concentrated in EU-domiciled holding structures, particularly Luxembourg and Netherlands vehicles. CRS continues to cover the majority of offshore financial account information. Behavioural response modelling should treat this as a scenario-analysis input, not a point estimate.
4.4 Structural and irreducible limits of the design
No items. JUR compiles data and maps institutions; it does not make design decisions that involve trade-offs.
4.5 Governing Council calibration parameters
No items in this paper.