Keir Starmer is 'unable' to defend Britain, his own Defence Secretary said on Thursday as he quit with a furious blast.John Healey accused the Prime Minister of being too weak to face down Rachel Reeves over the defence of the nation.Mr Healey revealed that plans signed off by the PM and Chancellor will increase defence spending by just 0.08 per cent of GDP by the end of the decade, despite rising threats across the world.Senior defence figures warned that the threadbare settlement would leave Britain 'in danger'.On Thursday, the Chief of the Defence Staff, Air Chief Marshal Sir Richard Knighton, was also on resignation watch. And Armed Forces minister Al Carns followed Mr Healey out of the door less than an hour after a Sky News interview – not authorised by No 10 – in which he said the funding proposals were not good enough.Despite the warnings, Sir Keir signalled he will stick with the funding plan rejected by Mr Healey as he scrambles to publish the long-delayed Defence Investment Plan (DIP) before he faces a leadership challenge.On Thursday security minister Dan Jarvis was appointed as Defence Secretary. The MP for Barnsley North served in the Parachute Regiment and was later deployed to Kosovo, Northern Ireland, Iraq and Afghanistan.In a blistering resignation letter, veteran defence secretary John Healey said Keir Starmer had proved 'unable' to defend the UKAl Carns (pictured) resigned on Thursday evening after criticising the Government's defence investment plan Ministers were told in December that the Ministry of Defence needed another £28billion by 2030 to implement last year's Strategic Defence Review, which is seen as the minimum required to keep Britain safe.But, after months of wrangling, Mr Healey was offered the equivalent of just £10billion over four years – less than the £12billion Ms Reeves found to reverse the cost of the two-child benefit cap over the same period. A last-minute Cabinet whip-round this week failed to deliver more money after Ed Miliband flatly refused to budge on his costly Net Zero plans.In a blistering resignation letter, Mr Healey said the final funding settlement 'falls well short of what is required for defence and the country at this dangerous time'.Sir Keir insisted the plan would provide the 'necessary resources' for defence in a way that is 'sustainable and fair', adding that Labour would 'provide the resources our military needs to keep us safe'.Kemi Badenoch said the Government was 'falling apart' and the PM's failure to cut the welfare bill was endangering the country.The Conservative leader said Sir Keir was 'too weak to cut welfare and fund defence'.Former Chief of the Defence Staff Nick Carter on Thursday said Labour's failure to properly fund the Armed Forces left Britain 'in danger'. And General Sir Richard Barrons, who co-authored the Government's defence reviewlast year, told the BBC the funding crisis 'makes this country unsafe, diminishes its place within Nato and makes it vulnerable to war in the 21st century.' He added: 'Our enemies as well as our allies will have observed this catastrophe today.'Former Navy chief Admiral Lord West said the Treasury 'needs to be kicked into shape', tellingThe i Paper: 'They've got to be told what to do. The Prime Minister is the First Secretary of the Treasury, after all.'If one ran a ship like that, it would be a bit of a disaster. You go aground, and then you'd sink.'To be quite honest, welfare and national health don't matter if there is a war and you lose it.'Earlier he said: 'I thought Keir Starmer understood, because he has said all the right words not just to us but also to other countries as well, yet clearly he can't tell his Chancellor what he wants in terms of spending the right money.' In an extraordinary intervention underlining the bitter rift at the heart of government, a Treasury source accused Mr Healey of wanting a return to austerity to fund defence. 'Let's be clear on what John is asking for: cuts to schools and hospitals,' the source said.Unimpressed: Rachel Reeves has privately described defence spending as a 'money pit'Al Carns wrote a letter to the Prime Minister criticising his Defence Investment Plan, calling it 'inadequate'The jibe drew a furious response from friends of Mr Healey, with some urging the PM to sack the Chancellor. 'Rachel has behaved appallingly,' said one ally. 'If anyone should go, it's her.'Labour sources said Mr Healey had a 'stand-up row' with Ms Reeves on Wednesday and decided to quit on Thursday after the PM sided with his Chancellor.As part of the Defence Investment Plan, Mr Healey had asked for a minimum of an additional £28billion on top of current defence spending.Despite £18billion being mooted as a compromise figure, the Chancellor is understood to have offered an uplift of a mere £10billion in real terms. The DailyMail's Don't Leave Britain Defenceless campaign has been pushing for a boost to spending for the Armed Forces.Before he also quit, Mr Carns, a decorated former Special Forces colonel, said the funding proposals were 'not fit for purpose'.The settlement on offer, Mr Carns added, 'isn't enough, and that's quite dangerous at a critical moment in the geopolitical situation that we live in'.Former Tory defence secretary Ben Wallace praised Mr Healey's 'principled' decision and told the Daily Mail: 'Rachel Reeves' refusal to put the security of the nation first put John Healey in an impossible decision. 'Ever since she took the reins at the Treasury she has prioritised spending on benefits and used accounting tricks to avoid the tough decisions needed to keep us safe.'Labour has trashed Britain's reputation in Nato and the failure to deliver the Defence Investment Plan has made us a laughing stock. His loyalty to his party and the PM was not reciprocated by them when it mattered. I wish him the very best.'Mr Healey's resignation came after an exceptionally rare intervention by Air Marshal Sir Richard, who wrote to the Prime Minister expressing concerns about level of defence expenditure being touted by the Treasury.The senior RAF officer warned that the Government's plans were inadequate and fell far short of what was needed to prepare Britain's Armed Forces for modern high-intensity conflict. John Healey seems to be laying the groundwork for a challenge to Starmer, writes Hodges (pictured together visiting British soldiers at a Nato base in Estonia, near the Russian border)Mr Healey's bombshell letter also threatens international repercussions for Sir Keir. Donald Trump has demanded that Nato countries increase defence spending to 5 per cent of GDP. But Mr Healey's letter warns it will increase from 2.6 per cent next year to just 2.68 per cent by the end of the decade.The two leaders are due to meet at next week's G7 summit in France, when defence is likely to be top of the agenda.Labour's refusal to publish the DIP has been blamed for UK defence manufacturers going bankrupt and destroying Britain's reputation inside Nato.While this country has led Europe in supporting Ukraine following Russia's illegal invasion four years ago, Britain has also been left behind on defence spending by allies, lagging some way behind Nato partners such as Poland and Baltic states.Hitting back at his critics on Thursday, Sir Keir said: 'I am proud of our record on funding. When we entered government in 2024 I took the decision to increase defence spending after the Conservatives hollowed out our Armed Forces.'The PM insisted the DIP 'will provide the resources our military needs to keep us safe'.