The Government's ambitious Defence Investment Plan (DIP), which pledges a £15bn increase in military spending over the next four years, is under close scrutiny regarding its funding mechanisms. While Prime Minister Sir Keir Starmer has hailed the plan as a "historic shift" for the nation's defence capabilities, critics suggest the new financial commitment may still be insufficient for national security. Attention has now shifted to the Treasury's revelation that identified departmental savings do not fully cover the planned defence spending rise, leading to discussions about a significant funding gap.
Initial reports highlighted a potential "£5bn defence black hole" over the four-year period, a figure that could present a considerable challenge for the presumed next Prime Minister, Andy Burnham. However, public finance experts, including those consulted by BBC Verify, advocate for a clearer interpretation of these figures. They argue that presenting budget shortfalls in annual terms offers a more accurate picture, preventing the exaggeration that cumulative totals over several years can create. By this measure, the funding shortfall for the DIP is estimated to be approximately £1.2bn annually.
This annual £1.2bn gap will need to be addressed in the forthcoming Budget, expected in the autumn. Should Andy Burnham assume the premiership, this would likely be his first Budget, requiring decisions on how to bridge the gap – whether through further spending cuts, tax increases, or additional borrowing. While £1.2bn represents a relatively small fraction of total Whitehall departmental spending (0.17% of projected £678bn in 2026/27) or total tax revenues (0.1% of £1,170bn in 2026/27), its significance becomes clearer when viewed against the Chancellor Rachel Reeves's fiscal headroom.
The Chancellor's Spring Statement in 2026 provided approximately £24bn in headroom against her fiscal rule of balancing day-to-day spending with tax revenues by the end of the Parliament. In this context, the £1.2bn annual shortfall accounts for around 5% of that leeway. Ruth Curtice of the Resolution Foundation noted on BBC Radio 4's Today programme that a figure of this magnitude can be substantial within the context of annual budget adjustments, sometimes exceeding the total new tax and spending measures outlined in Budgets a decade ago.
Ministers have contended that such funding gaps are not uncommon, citing precedents where spending commitments were made ahead of specific funding allocations in subsequent Budgets. Examples include Rachel Reeves's reversal of winter fuel payment cuts without immediate funding details, significant Covid-19 pandemic spending like the furlough scheme announced outside of a Budget, and former Prime Minister Theresa May's five-year NHS funding package, which left funding specifics to future spending reviews. Thomas Pope, chief economist at the Institute for Fiscal Studies (IFS), supports this view, stating that such situations are "not that unusual."
Source: BBC Verify, The Treasury, Resolution Foundation, Institute for Fiscal Studies