Rachel Reeves and Sir Keir Starmer have been slammed for a failure to provide defence with a substantial cash injection as a former Nato secretary general said an “ever-expanding welfare budget” would not keep the UK secure. Downing Street has come under fire for its delay in setting out a clear timeline for an uplift in defence spending, with the Labour government putting the country “in peril” by failing to set out its plan. Lord George Robertson, the former Labour defence secretary who headed Nato and co-authored the strategic defence review, took aim at “non-military experts” in the Treasury for “vandalism”.

He told the Financial Times that “we cannot defend Britain with an ever-expanding welfare budget” and took aim at the Prime Minister, claiming he was “not willing to make the necessary investment”. Robertson will speak at a lecture in Salisbury on Tuesday evening to warn that the Iran war should be a “rude wake-up call” for the government and said the UK was “underprepared”. His intervention will have left government ministers stung given Robertson’s review underpins the future of defence in the UK.

City AM analysis showed that the UK is drifting away from a Nato target to spend 3.5 per cent of GDP on defence by 2035. The analysis also showed that the UK was falling far behind the likes of Russia and China in military spending while Nato members were more vulnerable to hostile countries when the US’ military expenditure was not accounted for. Senior officers in the armed forces have warned that there is a £28bn shortfall over the next four years for spending on necessary plans due to surging costs.

Ministers had been due to publish the Defence Investment Plan by autumn last year but details of the 10-year strategy on how to use resources have not been unveiled. Starmer said he needed to know “where the money’s coming from” before committing to a timeline for higher defence spending. Defence spending suffering from ‘corrosive complacency’ Key findings in Robertson’s review last year included an admission that the UK was not ready for war and called for leaders to avoid “complacency about defending our country”.

But in a speech on Tuesday, Robertson will attack ministers for a “corrosive complacency”. Robertson also did not spare attacks for opposition leaders, suggesting that political point-scoring on defence was “a dangerous luxury”. He will say in a speech later on Tuesday: “There is a corrosive complacency today in Britain’s political leadership. Lip service is paid to the risks, the threats, the bright red signals of danger — but even a promised national conversation about defence can’t be started.” He will also hit out at Reeves’ lack of focus on defence in set-piece speeches as she has appeared to give the armed forces little mention.