Britain is facing increasing challenges in raising tax revenues without undertaking significant reforms to its tax system, according to warnings from the International Monetary Fund (IMF) and the country’s fiscal watchdog. As Chancellor John Healey prepares to deliver his first Budget, experts caution that the scope for further tax increases is narrowing unless fundamental changes are implemented.

The UK’s overall tax burden remains lower than that of many advanced economies, including France, Germany, and Italy, based on revenues relative to economic output. However, recent freezes on income-tax thresholds since 2022 and tax hikes introduced from 2024 have pushed the tax burden to its highest level in the post-war era. Recent IMF data shows the gap between UK and European Union government revenues as a share of GDP has shrunk to its narrowest on record.

The UK’s tax system stands out for its high property-related tax revenue relative to GDP, ranking highest among 38 OECD countries. Yet, the overall structure is criticized for its complexity and inefficiency. Stuart Adam, a senior fellow at the Institute for Fiscal Studies, points to an excessively long tax code and a convoluted framework of VAT exemptions as examples of design flaws. Tax competitiveness rankings from the Tax Foundation place the UK near the bottom among wealthy countries, particularly noting poor design and high rates in property taxation.

Economists emphasize that the UK’s fiscal challenges are driven more by the tax code’s structure than by insufficient revenue. Alex Mengden of the Tax Foundation notes that while most nations have some tax difficulties, the UK faces systemic issues across the board. Arun Advani, a professor at the University of Warwick, echoes this view, describing the UK system as simultaneously problematic in multiple areas.

Higher earners are disproportionately affected by income taxes, with rates exceeding the OECD average, and even more so at the top end. The system includes sharp tax “cliffs,” such as the tapering of the £12,570 personal allowance for incomes above £100,000 and the withdrawal of childcare benefits, which can create marginal rates that disincentivize additional work. In contrast, social security contributions in Britain are relatively low compared to other countries, partly because pension provision relies more heavily on voluntary schemes like automatic enrolment rather than large public systems funded by social contributions, as seen in Germany, France, and Italy.

The Office for Budget Responsibility (OBR) has flagged that raising tax rates further within the current framework risks economic distortions. The IMF has echoed concerns that funding the UK’s spending needs solely through higher taxes could hinder growth and lead to behavioral responses that reduce the expected revenue gains. Tax increases on capital income are especially problematic due to avoidance risks, as assets can be shifted across borders. Chancellor Healey has rejected proposals to align capital gains tax rates with income tax to maintain the UK’s appeal to investors. The IMF also warns that higher taxes on labor might provoke significant declines in labor supply.

Labour’s 2024 election manifesto further constrains tax-raising options by pledging not to increase taxes on working individuals, including income tax, national insurance, or VAT. It also rules out hikes to corporation tax. Tax analysts say this limits the government’s ability to generate revenue, forcing a reliance on numerous minor adjustments rather than comprehensive reform.

In sum, authorities and experts agree that the UK is approaching the limits of what can be achieved through conventional tax increases without undertaking major systemic reforms to enhance efficiency, fairness, and economic growth.