A UK Wealth Tax Demands Fiscal Policy Architecture, Not Short-Term Budgetary Fixes

León Fernando Del Canto : Barrister (Lincoln’s Inn) and Abogado (ICAM); International Private Client Counsel and member of the Private Client practice group at Outline Chambers in London.

The Times' headlines this week have been unmistakable: "UK wealth tax no longer looks so distant." With the Green Party pushing Labour leftward and momentum building in California for the 2026 Billionaire Tax Act, the conversation is often framed as a local political weathervane. However, to view this purely through a domestic lens is to miss the broader shift. This is the British expression of a global trajectory I have termed Pillar 3 : the emerging international consensus that, following the OECD’s Pillars 1 and 2, private wealth is the next frontier for tax authorities.

As I have stated previously in the Financial Times, the choice between taxing private wealth and cutting essential services is no longer just an economic dilemma; it is a political and moral reckoning. It is becoming increasingly difficult to justify sacrificing safety nets for the vulnerable while vast pools of untaxed wealth remain untouched.

Yet, I do not approach this as a defender of untaxed capital. I approach it as a practitioner who has spent twenty years in cross-border practice watching how badly wealth taxation can go when it is designed with haste: and how productive it can be when built with care. The UK is currently in danger of adopting the worst possible version of it: an impulsive, unilateral levy at a moment when its competitive landscape is already fragile.

This is the real choice. Not "tax the rich or do nothing," but architecture versus impulse.

The Pillar 3 Frame: The Global Shift

In my work for Taxation magazine, I argued that three forces are pushing wealth taxation to the top of the international agenda.

First, the corporate tax base has been weakened by decades of international competition. Second, wealth concentration has accelerated, fueling mainstream political movements. Third, the mobility of corporations makes them difficult to pin down.

Against this backdrop, global assets under management are projected to reach roughly $145.4 trillion by 2025.

The OECD’s Pillars 1 and 2: reallocating profits of multinationals and introducing a 15% global minimum tax: proved that when tax bases are threatened, states can cooperate. A coordinated Pillar 3 framework would build on this. It would establish minimum standards for taxing assets above specific thresholds, harmonise inheritance rules to close loopholes, and coordinate exit taxes for mobile individuals.

The key here is coordination. Wealth taxation, to be effective in a world of mobile capital, must be architectural rather than improvised.

What the UK Risks: The Danger of Improvisation

What the UK Risks: The Danger of Improvisation

The current UK debate is troubling because it is happening in the abstract. The Green Party proposes a 1% annual wealth tax on net assets above £10 million, while Labour reportedly considers more modest versions for the coming Budget cycle.

My concern is not the proposition that the wealthiest should pay more, but that the proposition ignores the design parameters that determine success. A wealth tax can either raise real revenue or simply accelerate capital flight. Without engagement with valuation difficulties, behavioural elasticities, and enforcement costs, the policy is merely political theatre.

The 2020 Wealth Tax Commission was clear on these points. It actually came out against an annual wealth tax in the UK, citing administrative complexity and the disproportionate cost of enforcement. While it was qualifiedly in favour of a one-off levy, it tied that endorsement to the exceptional fiscal shock of Covid-19. To invoke that endorsement now, in a period of "ordinary" fiscal pressure, is to misuse the evidence.

The 2025 Non-Dom Reforms Have Reset the Bargain

We must also acknowledge the reality of the post-2025 landscape. The Finance Act 2025 has already dismantled the centuries-old non-domiciled regime, replacing it with the Foreign Income and Gains (FIG) regime. This residence-based system already brings worldwide assets within the scope of UK Inheritance Tax for long-term residents.

In effect, the United Kingdom has already moved unilaterally and aggressively to tax global wealth. Whether the projected £12.7 billion in revenue materialises depends on behavioural responses that are still being debated. Reports of thousands of millionaires fleeing the UK must be read with skepticism, but the directional risk is real. This uncertainty is precisely why we need fiscal caution, not further experimentation with an impulsive wealth tax.

What Coherent Architecture Would Require: Six Essential Features

What Coherent Architecture Would Require: Six Essential Features

If a wealth-based levy becomes unavoidable, we must move the question from whether to how. Drawing on comparative evidence from Switzerland, Norway, and the Spanish model found at the official Spanish Tax Office (AEAT), a coherent UK wealth tax would require six non-negotiable features:

1. An Income-Linked Ceiling

The Spanish system (Article 31 of Law 19/1991) caps the combined liability of wealth tax and income tax at 60% of the income tax base. This prevents the levy from becoming confiscatory during years of low investment returns: the primary driver of capital flight. A UK design must include a floor-and-ceiling mechanism to remain defensible.

2. A High Entry Threshold

Any threshold below £5 million would likely capture asset-rich but cash-poor middle-class households, such as long-term homeowners in London. A threshold of £10 million is far more administratively defensible and targets the intended demographic without causing broad political backlash.

3. Properly Delineated Reliefs

We must protect the "habitual residence" up to a specific cap and include business asset reliefs. Without these, a wealth tax becomes a tax on entrepreneurship and intergenerational continuity, forced liquidations of family businesses would be the unintended consequence.

4. A Credible Valuation Framework

Reliance on the Valuation Office Agency (VOA) for property and listed market prices for securities is essential. Crucially, taxpayers must have a meaningful right to challenge valuations. The implementation costs: estimated between £600 million and £3 billion: must be acknowledged before the first draft is written.

5. Liquidity Safeguards

The regime must allow for instalment payments or deferrals for asset-rich/cash-poor cases. Provision for payment in kind, particularly for heritage assets, prevents the regime from destroying the very assets it seeks to tax.

6. A Sunset Clause and Non-Confiscation Principle

If a levy is intended to be one-off, it must be drafted as such. If recurring, it must be subject to periodic review and a statutory non-confiscation principle. Spanish jurisprudence (STC 149/2023) has established that no levy on capital may exhaust the "patrimony" itself. This is a limit the UK must internalise.

Spain as Both Source and Warning

As a dual-qualified practitioner, I am often asked if the Spanish model is a template. It is both a source of ideas and a stern warning. Spain’s wealth tax (Impuesto sobre el Patrimonio) is a state tax devolved to Autonomous Communities. When Madrid applied a 100% rebate, the central government responded with the "Solidarity Tax" (ITSGF) to override it.

This has resulted in a constitutional arms race, migration of taxpayers between regions, and permanent political instability. While the UK’s unitary system wouldn't face regional disputes, it would inherit every other tension: valuation disputes, avoidance behaviour, and political volatility. Spain proves that even with developed infrastructure, wealth taxation is fraught with risk.

Conclusion: Architecture Over Impulse

Conclusion: Architecture Over Impulse

The global Pillar 3 trajectory is real, and the moral reckoning regarding wealth concentration is unavoidable. However, the proper response is not to rush into a unilateral, impulsive domestic levy.

The choice is between a wealth tax built in a single Parliament in response to short-term political pressure: which will inevitably damage fiscal stability: and a wealth tax built carefully. The latter must be integrated into emerging international architecture and grounded in robust evidence.

If the political settlement after the next election demands a wealth levy, the six design features I have outlined are the bare minimum for a serious Bill. Anything less is an experiment whose costs will be borne by the very people the levy was meant to protect.

Author Bio

León Fernando Del Canto is a Barrister of Lincoln’s Inn (practising from Outline Chambers, 6 Pump Court, Temple) and Abogado of the Ilustre Colegio de Abogados de Madrid. He is a PhD researcher at the Institute of Advanced Legal Studies, University of London, and a regular contributor to major financial publications on cross-border tax matters.