UK Budget Headroom Shrinks by £12bn Amid Iran War Inflation

The UK’s new fiscal outlook shows a dramatic cut in the Chancellor’s budget headroom, down to about £12bn from £23.6bn, largely due to higher borrowing costs triggered by the Iran war and weaker growth. With limited room to support growth or the cost of living, Healey may need to consider tax rises…

By Felo News Desk · Published Mon, 21 Sep 2026 11:10:24 GMT

The UK government’s fiscal outlook has been sharply revised, leaving Chancellor John Healey with a markedly reduced budget headroom before the October 28 Budget. According to a new KPMG economic outlook, the headroom – the difference between projected revenue and spending – has fallen to roughly £12 billion from the £23.6 billion forecast in the spring. The shortfall is largely attributed to soaring borrowing costs linked to the Iran war and a slowdown in economic growth.

What Happened?

In a report released this week, KPMG highlighted that the UK’s borrowing costs have surged as investors demand higher yields on gilts amid fears that the Iran war will fuel inflation. The higher yields have already eroded about £9 billion of the government’s fiscal headroom. A further £2 billion is expected to be lost as the Office for Budget Responsibility (OBR) is likely to downgrade the country’s fiscal outlook, reflecting weaker growth.

These developments mean that the Chancellor will have limited flexibility to provide significant support for growth or to ease the cost of living when he presents his first Budget as Chancellor. KPMG warned that restoring the previous level of headroom could require either tax rises or spending reductions, although the government has pledged not to raise taxes on working people.

Why the Iran War Matters

The Iran war has triggered a sell‑off in UK government bonds, pushing long‑term interest rates higher. KPMG projects that UK interest rates will climb from 3.75% to 4% in November, before easing back next summer as the impact of energy prices on inflation fades. Inflation, which stood at 3.1% in August, is forecast to rise to about 3.5% in the autumn and peak near 4% in the first quarter of next year.

Higher borrowing costs increase the cost of servicing public debt, which in turn squeezes the budget. The combination of a gilt sell‑off and inflationary pressures has left the government with less fiscal space than previously expected.

Growth Outlook and Its Impact

Growth is also a key factor in the tightening headroom. KPMG predicts overall growth of 1.3% in 2026, with a slowdown in the final six months of the year as inflation weighs on household spending. Growth is expected to edge up to 1.4% next year. Slower growth means lower tax receipts, which further reduces the budget headroom.

With both higher borrowing costs and weaker growth, the government’s ability to fund new initiatives or support the economy is constrained. This could force the Chancellor to consider alternative measures, such as changing the tax structure or cutting discretionary spending.

What Happens Next?

As the October 28 Budget approaches, the government will need to decide how to balance the twin priorities of supporting growth and managing the cost of living. The KPMG report suggests that the Chancellor may have to look beyond traditional tax increases on working people, potentially exploring other tax measures or spending cuts.

Stakeholders, including businesses and households, will be watching closely to see whether the government can maintain its commitment to not raising taxes on working people while still addressing the fiscal shortfall. The OBR’s forthcoming review and the government’s policy decisions will shape the final budget outcome.

Key facts

Fiscal headroom cut to £12bn from £23.6bn
Higher borrowing costs driven by Iran war
Inflation projected to rise to 4% next year
Growth forecast at 1.3% in 2026
Chancellor may need tax rises or spending cuts
Government committed to no tax hikes on workers
Budget due 28 Oct

Why it matters

A shrinking fiscal headroom limits the government’s ability to support growth and manage living costs, potentially impacting households and businesses across the UK.

Frequently asked questions

What is fiscal headroom?

Fiscal headroom is the difference between projected government revenue and spending; it represents the space the government has to operate without borrowing.