Greens set out first detailed numbers for proposed bank windfall tax

The Green Party of England and Wales has published the first detailed figures for its proposed windfall tax on big banks, setting a 38% rate on UK domestic profits above £800m and directing the revenue towards National Insurance cuts for small and medium-sized businesses.

Green Party leader Zack Polanski said the tax would raise at least £19bn a year and would be used to cut tax bills for a million smaller companies by doubling the Employment Allowance — a mechanism that reduces how much employers pay in National Insurance — by up to £10,500 per firm. The campaign group Positive Money, which first suggested the idea, produced the £19bn revenue estimate the Greens have adopted (BBC News).

The party's official announcement was published on its website on August 19, 2026, with the BBC reporting on the policy on August 20 (Green Party). This is the first time the Greens have attached specific numbers to the bank windfall tax, after Polanski previously argued that banks are "ripping off customers" and should pay more tax (BBC News).

Polanski said the UK's biggest banks are regularly making record-breaking profits, not from improved services or products, but from high interest rates set by the Bank of England to curb inflation. The framing positions the tax as reclaiming gains that arose from monetary policy decisions rather than from commercial innovation (BBC News).

A windfall tax is a one-off levy on profits that arise from external circumstances rather than a company's own efforts — in this case, the Bank of England's interest rate decisions rather than new banking products or better service.

The bank levy is the latest in a series of windfall tax proposals the Greens have advanced. In a major speech on March 18, 2026, Polanski set out plans for a 1% tax on wealth over £10m and 2% on wealth over £1bn, which he said would raise around £15bn per year. In the same speech, he called for a "real, loophole-free windfall tax with no exemptions for reinvesting in fossil fuels" that "claws back every single pound" (Green Party). The party's June 2024 manifesto pledge committed to advocating windfall taxes where there is evidence that market distortions are creating risk-free additional profits (Green Party.

Polanski has also targeted fossil fuel companies. After Barclays reported quarterly profits of £3.3bn on July 28, 2026, up 31% year on year, Polanski joined calls for banks making "eye-watering" profits to help families with the cost of living (Green Party). In April, he said on his Facebook page that "under pressure, they finally announced they would put forward a windfall tax on the obscene profits being raked in by fossil fuel companies" (Facebook). He has separately called for oil and gas companies that made bumper profits during the Iran war to be taxed at a higher rate (Financial Times).

The bank windfall tax proposal faces industry resistance. When a similar idea was raised last year, the trade body UK Finance said banks already pay both a corporation tax surcharge and the bank levy (BBC News). The Treasury's existing bank-specific tax architecture, comprising the bank levy and the 8% corporation tax surcharge on banking profits, means any additional levy would sit on top of those mechanisms rather than replace them.

The Labour government's response has been to point to its own small-business measures. A Labour Party spokesperson said Labour is cutting business rates for nearly 32,000 small businesses and working on a renaissance for Britain's high streets (BBC News).

The policy applies to England and Wales, where the Green Party of England and Wales operates. Corporation tax is reserved to Westminster, so the proposal would require UK legislation. Business rates and aspects of business support are devolved to Scotland, Wales and Northern Ireland, meaning the framing around SME relief would interact differently with devolved administrations — the Scottish Parliament, the Welsh Senedd and the Northern Ireland Assembly at Stormont — depending on the mechanism chosen.

The broader context here is a party building a coherent revenue-raising architecture. The wealth tax, the fossil fuel windfall tax and now the bank windfall tax share a common logic: identifying profits the Greens characterise as unearned, arising from macroeconomic conditions or market distortions rather than enterprise, and redirecting them to households and small businesses. The £19bn bank levy and the £15bn wealth tax together would represent a substantial fiscal expansion if implemented, though neither has government backing and both remain opposition proposals.

What remains unclear is how the 38% rate interacts with the existing corporation tax surcharge and bank levy in practice, whether the £800m threshold would capture only the largest high-street banks, and whether the Employment Allowance doubling would be delivered through the tax system or through a separate grant mechanism. These are the design questions that would determine whether the £19bn revenue estimate holds up under scrutiny.