Keir Starmer suffered another hammer blow today as John Healey dramatically quit the Government, accusing him of failing to 'defend the country'.The defence secretary announced he was resigning with a brutal parting shot at the PM and Chancellor Rachel Reeves after months of bitter wrangling over military funding.Mr Healey said he could not accept the settlement in the Defence Investment Plan because it fell 'well short of what is required' at a 'dangerous time'. He suggested the proposals would only boost military spending from 2.6 per cent of GDP next year to just 2.68 per cent in 2030, despite the 'imperative to speed up readiness to fight'. That is equivalent to around £10billion extra, about a third of what had been pleaded for. Swiping at Sir Keir and the Chancellor, Mr Healey said: 'You have been unable, and the Treasury has been unwilling, to commit the resources that the nation needs to defend the country at this time of rising threats.' As Sir Keir's grip on power loosened again, allies of Andy Burnham immediately praised Mr Healey's 'principled' stance, saying his 'integrity is beyond question'. Labour former defence secretaries Lord Hutton and Geoff Hoon broke cover to brand the situation a 'car crash' and urge MPs to drop their opposition to curbing welfare to free up cash.Extraordinarily, a Treasury source suggested Mr Healey had been effectively demanding cuts to schools and hospitals, arguing that Ms Reeves 'will always do what is right and needed to keep this country safe'. In his reply to Mr Healey's resignation letter, Sir Keir insisted the Defence Investment Plan would keep Britain safe as he rejected suggestions he is skimping on military spending.The PM said the plan would deliver 'an unprecedented increase in defence spending in a sustainable way' and give the Armed Forces 'necessary investment', but suggested going further or faster would require 'irresponsible borrowing'.A Government source had earlier tried to shore up Sir Keir's premiership this afternoon, saying the 'country is safe' because of the decisions he had made. 'We cut the international aid budget to make record investment in our armed forces, and now the PM is imposing cuts on other government departments to fund billions more,' the source said. However, Mr Healey's deputy Al Carns has also warned the plan is not 'fit for purpose', saying Sir Keir has 'got to sort this out'. The Defence Secretary had been due to visit Gosport with the Australian deputy PM this morning, but had a showdown with Sir Keir in London instead - then quit. Downing Street is still scrambling to find a replacement, with security minister Dan Jarvis among those tipped for the job. No10 had hoped the blueprint to modernise the military and shore up budgets could finally be unveiled this morning, ahead of the PM meeting fellow leaders at an international summit next week.However, that prospect was humiliatingly dashed as the Treasury and Cabinet ministers play hardball over how to find the funding.The PM's inability to get the measures over the line highlights his waning authority, with Mr Burnham widely expected to mount a challenge if he wins the Makerfield by-election next week. One gloomy Government aide told the Daily Mail there would be no end to the 'paralysis' until Sir Keir is replaced.Kemi Badenoch said it was proof Sir Keir's 'premiership is falling apart'. 'He can't run the country. He is paralysed because his backbenchers only want to spend money on welfare,' she said.