Defence minister Al Carns quit tonight as he accused Labour of 'failing' Britain's Armed Forces, saying he could not 'in good conscience' back the Defence Investment Plan (DIP). 

The Armed Forces minister followed his boss, Defence Secretary John Healey, out of the door as he said the long-delayed document was 'not built for the threat we face'. 

The latest resignation by the decorated former marine was swiftly followed by an announcement from Number 10 that Dan Jarvis would be replacing Mr Healey as the new Defence Secretary. 

Sir Keir Starmer insisted in his first statement since the crisis began on Thursday that the Government would 'give our armed forces the capabilities they need to defend Britain and keep our nation secure'. 

Mr Carns said in his resignation letter to the Prime Minister: 'We owe those who serve the UK the kit to do the job and the loyalty to stand by them when it's done. We are failing on both.' 

He added that he could not stand up in Parliament and defend 'a level of investment I know to be inadequate to the task'.

'We are asking our armed forces to operate in a more dangerous world on a budget written for a calmer one,' he said. 

'A serious country funds its defence to meet the threat it actually faces, not the threat it wished it faced.' 

On his exit from Government, Mr Healey is understood to have asked other defence ministers to remain in post.

Mr Carns, 46, who served as an adviser to three UK defence secretaries, initially indicated he was willing to wait until the DIP was finalised before considering his position in Government.

But just an hour later, he reversed that decision and resigned - as did Pamela Nash, Mr Healey’s parliamentary private secretary.

She described the 'delays and difficulties' which had dogged the DIP as 'the latest issue that is damaging to the trust of the public in us', in a resignation letter to Sir Keir. 

Mr Carns, who previously announced his own leadership ambitions and said he would stand in a contest to replace Starmer, continued: 'The character of conflict is changing faster than our procurement can keep up with. 

'We are still purchasing capability suitable for the last war while our adversaries arm for the next one.

'We need a new way of governing and we need it now.'

He also criticised the Northern Ireland legacy bill as well as department in-fighting. 

More widely, Mr Carns took aim at the Labour Government's overall workings, writing: 'The machinery of government itself has been left to decay. Decisions that should take days take months.

'Departments fight each other instead of the problem. Officials and ministers who know the truth are not always rewarded for telling it.'

He concluded: 'I'll keep fighting for the people I served with. I hope this government will too.'

Mr Carns' resignation follows that of Mr Healey, Britain's defence secretary, earlier today, after he also accused the Prime Minister 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.' 

Late on Thursday night, Number 10 announced Dan Jarvis would be John Healey's replacement. 

Mr Jarvis, who previously served as the security minister in the Home Office, served as an officer in the Parachute Regiment from 1997 to 2011. 

The former Army officer has been MP for Barnsley North since 2011, and has been deployed to Kosovo, Northern Ireland, Iraq and Afghanistan. 

In his first statement since the crisis began today, Sir Keir said: 'My first duty is to keep the British people safe, and I will always do what is necessary to protect our national security.

'I am pleased to appoint Dan Jarvis as defence secretary as we strengthen our armed forces and meet the growing threats facing our country.

'This Labour government is delivering the largest sustained increase in defence spending since the Cold War.

'In a dangerous and volatile world, we will give our armed forces the capabilities they need to defend Britain and keep our nation secure.'

As Sir Keir's grip on power loosened today, 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.

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'. 

She said: 'He can't run the country. He is paralysed because his backbenchers only want to spend money on welfare.'

Reacting to the two resignations today, former Tory defence secretary Ben Wallace said: 'Al was one of my very best commanders when I was in post. The MoD needs him.

'This government needs his knowledge and leadership. If No 10 won't listen to him and [former defence secretary John] Healey, we really are screwed.'