Chancellor John Healey will deliver his first Budget on 28 October, a test of Prime Minister Andy Burnham’s priorities, according to the Institute for Government – however, Britain’s defence ambitions face an increasingly difficult financial backdrop.

Figures released by the Office for National Statistics on 21 October show that September borrowing reached £24.5 billion, £1.9 billion above forecast, while debt interest cost £10.9 billion. The Institute for Fiscal Studies (IFS) estimates that interest already consumes roughly £1 in every £13 of government spending.

Britain’s Existing Defence Commitments

The Ministry of Defence and Treasury’s Defence Investment Plan provides an additional £15 billion between 2026–27 and 2029–30, bringing planned defence investment across those four years to £298 billion. According to the government, core NATO defence spending will reach 2.7% of GDP in 2027–28. Britain has also committed to 3% in the next Parliament and 3.5% by 2035. How the longer-term targets will be financed remains unresolved.

The £4.7 Billion Funding Question

Of the £15 billion increase, the Treasury has identified funding sources for £10.3 billion, mainly through reprioritising departmental budgets. A September parliamentary answer specified contributions from transport and energy budgets.

Speaking to MPs on 13 October, Defence Secretary Wes Streeting acknowledged the shortfall: “There was a £4.7 billion gap, which needs to be plugged at this Budget for the immediate term.”

Further savings, taxes or borrowing could potentially cover the remainder, but no final decision has been announced. IFS economist Max Warner has warned that additional defence funding carries consequences for other public spending, taxation or borrowing. The central question is not simply how much Britain can spend on defence, but what other priorities may have to give way.

Where Is Britain Investing in Defence?

Already announced priorities include £790 million for air and missile defence, £11 billion for munitions and weapons, more than £5 billion for drones and autonomous systems, and £2.5 billion for cyber and electromagnetic capabilities.

Yet procurement is already facing constraints. Data from the National Infrastructure and Service Transformation Authority show that the planned whole-life budget for the Mechanised Infantry programme, which includes Boxer vehicles, fell by about £1.86 billion.

In a 14 October parliamentary answer, defence minister Luke Pollard confirmed that three proposed capabilities, including repair and recovery vehicles, would no longer be pursued. The Army is considering alternatives; 623 Boxer vehicles were already under contract. The changes highlight the tension between military modernisation and spending limits.

Political Pressure and the Cost of Rearmament

The government argues that stronger defence is necessary while maintaining fiscal discipline. Conservatives are demanding sharper cuts. Reuters reported on 20 October that party leader Kemi Badenoch proposed immediate welfare savings to help fund defence and reduce borrowing.

“Let’s cut spending. Let’s live within our means, and let’s bring in policies that will actually grow our economy,” she told reporters.

Labour also wants lower welfare spending, but favours helping more people into work. Meanwhile, IFS director Helen Miller warned against spending plans that rely on cuts ministers might not deliver: “Simply pencilling in implicit cuts that he has no intention of delivering would make the Budget a work of fiction.” The political disagreement is not only over rearmament, but who ultimately pays for it.

What Will the Budget Actually Reveal?

On 28 October, the government is expected to explain how it will cover the £4.7 billion gap. But according to a September Treasury answer to Parliament, the timetable for reaching 3% of GDP and the path to the 3.5% target in 2035 will come at the next Spending Review. The Budget will therefore be an early test of whether Britain’s financial plans can match its military ambitions.