UK ‘Windfall’ Bank Tax Would Worsen an Already Complex System

The prospect of a new tax on UK banks is back on the political agenda. Campaigners are calling for a “windfall” tax following strong reported profits from the UK’s largest banks, while industry representatives have warned that additional taxation could affect lending, investment, and the UK’s competitiveness as a financial centre.

This blog is based on an article written by Adam Craggs and Jasprit Singh that was published in Bloomberg Tax on 25 August 2026. Copyright 2026 Bloomberg Industry Group, Inc. (800-372-1033) www.bloombergindustry.com. Reproduced with permission.

Introduction

Any new tax measures would sit alongside other existing taxes. UK banks currently pay corporation tax at 25%, a 3% banking surcharge on relevant profits above the £100 million ($135.6 million) group allowance, and the bank levy (which is expected to raise around £1.4 billion in 2025/26).

The introduction of another bank tax or charge would add an additional layer to an already complex sector-specific tax regime. The economic consequences would depend not simply on the rate, but also on how banks respond to any such additional business cost.

Wider economic consequences

While the immediate political question is whether banks should pay more, it is also important to consider the practical issues of any new UK bank tax. A new targeted tax on UK banks could have effects beyond the additional revenue collected. Increasing the cost of doing business in the UK may influence where banks focus their activities and the attractiveness of the UK relative to other global financial centres.

Those considerations are particularly relevant given the international mobility of banking businesses. JP Morgan Chase CEO Jamie Dimon has reportedly warned the Prime Minister that higher bank taxes could have “adverse consequences”.

The impact may also be felt by customers. Depending on the design and competitive environment, banks may seek to recover some of any additional business cost through pricing, potentially affecting borrowing costs, deposit returns, or lending capacity.

For investors, predictability is important. Changes to sector-specific taxation may increase the uncertainty attached to long-term investment decisions, even when the ultimate tax rate remains competitive. The combination of these factors has the potential to distort the UK market and undermine the UK’s competitiveness as an international financial centre.

What would be taxed under a new UK bank tax? 

The tax base would be critical. A charge on banks’ profits would raise different issues from one based on balance sheet values, or a defined measure of excess returns.

Once there is more clarity from the Chancellor, it would be prudent for banks to consider how each potential model could apply across different business lines and entities, including UK subsidiaries, branches of overseas banks, and groups with both banking and non-banking activities.

The existing regimes demonstrate the complexity that could arise. The banking surcharge contains detailed rules governing the calculation of surcharge profits, group relief, losses, and anti-avoidance.

Similar questions could arise under any new taxing regime. For example, how are losses to be treated? What deductions are available? How are group companies to be treated? Can allowances be shared? How are cross-border activities attributed to the UK?

How would a new UK bank tax interact with existing taxes? 

A further charge would not operate in isolation. The introducing legislation would need to address its interaction with the banking surcharge and bank levy, including whether existing allowances are relevant and whether one charge effectively increases the base for another.

This is likely to be another important area for modeling. Two apparently similar proposals could produce materially different effective tax rates when the interaction with existing rules is taken into account. Again, once there is greater clarity from the government, banks may wish to consider modeling not only the headline rate but also the combined effective burden under different potential scenarios.

What are the potential areas of tension? 

From a legal perspective, the mechanics of any new legislation and how it would operate in practice would be of particular concern to banks. Sector-specific taxes are especially susceptible to disputes where legislation relies on broad concepts, detailed computational rules, or judgment-based allocation.

Potential areas of dispute include:

• Whether an entity or activity falls within the charge
• Calculation of taxable or chargeable profits
• Allocation of income and expenditure between UK and overseas operations
• Treatment of intragroup transactions
• Application of exemptions and thresholds
• Treatment of losses
• Whether anti-avoidance provisions apply

Legislation introducing any new tax or charge is also likely to contain targeted anti-avoidance provisions to prevent arrangements designed to avoid the tax or charge. Where significant restructuring or business-model changes are contemplated, contemporaneous evidence recording the commercial rationale for those changes is likely to be paramount if the bank’s tax treatment is later challenged by HMRC.

Overall, the experience of the existing regimes suggests that the legislative drafting would need to be precise to minimise the risk of potential disputes.

Practical steps

The period between formal announcement of any new measures and implementation is likely to be critical. Banks, affected businesses, and advisers, should consider:

• Scenario modeling: Quantify the potential impact under different tax bases, rates, and thresholds rather than focusing solely on the headline proposal.
• Legislative monitoring: Identify early how draft legislation changes the scope of the charge, particularly during any consultation process and parliamentary amendment to the draft legislation.
• Existing tax review: Map the proposed tax against the bank levy, banking surcharge, corporation tax, and relevant international tax rules.
• Transaction review: Identify significant restructurings, acquisitions, disposals, or changes in business models that could be affected by commencement or transitional provisions.
• Dispute readiness: Identify areas where the legislation is likely to require judgment and ensure that relevant calculations, assumptions, and the commercial rationale for transactions are appropriately documented.

The policy debate may be about raising additional revenue. The legal debate will be about certainty. For policymakers, the priority should therefore be a regime that is targeted, proportionate, and capable of being applied consistently.

For banks, the priority should be understanding the effective impact before the legislation is finalised and identifying potential areas of uncertainty.