The Treasury has not yet carried out any analysis of the trade-offs required for the UK to meet its Nato pledge to spend 3.5% of GDP on defence by 2035, its chief secretary Lucy Rigby has admitted. Under questioning from a joint session of the Treasury and defence committees, Rigby repeatedly insisted that funding decisions would be a matter for "the next prime minister" and the next spending review, drawing sharp criticism from MPs who noted that she oversees all public spending. The lack of a clear funding path matters because it was among the reasons cited for the resignation of defence secretary John Healey, and it leaves a major commitment unbacked by concrete plans.

MPs highlighted the scale of the challenge, with Bobby Dean noting the target would require an extra £30-40bn, equivalent to 3p to 4p on all rates of income tax, prompting Rigby to say a debate on "public consent" would be needed. The government has an interim goal of 3% of GDP in the next parliament, though the path remains unset and is deferred to the spending review due in mid-2027, by which point Andy Burnham is expected to be prime minister. Healey resigned ahead of the defence investment plan, which added £15bn over four years to reach 2.7% of GDP, while Rigby conceded a further £4.7bn must be found in the autumn budget; committee chair Meg Hillier likened the fund-later approach to the "£22bn black hole" Labour previously attributed to its predecessors.