The dramatic resignation of John Healey over the defence spending row has sent shockwaves through the government.
Widely viewed as one of the most dependable members of Sir Keir Starmer’s top team, he is a Labour loyalist, who had never, until now, publicly rocked the boat.
He was also highly successful at steering the Ministry of Defence through a time of huge and growing international unrest, shepherding support for Ukraine during the ongoing conflict with Russia and steering the UK’s response to Donald Trump’s war on Iran.
Replacing him would be a difficult job in normal times, even if Sir Keir was not facing a possible challenge to his own leadership from Greater Manchester mayor Andy Burnham.
But Mr Healey’s resignation letter was scathing about the government, and in particular, the Treasury’s attitude to defence spending.
Who Sir Keir appoints as his next defence secretary could reveal much about the support the PM still commands from his own MPs – and his vision for his government.
The Scotland secretary is already in the cabinet and is known to have ambitions beyond his current role.
A former minister in the last Labour government, he is a hugely experienced politician who would be seen as a safe pair of hands.
The current Armed Forces minister is a former Royal Marine who served five tours of Afghanistan. He was awarded the Military Cross for gallantry displayed in the conflict, and is still seen as an ‘action man’ – last year he climbed Everest, aiming to raise more than £1m for military charities.
He would be a popular choice for the role among Labour MPs.
But could he really sign up to a defence investment plan that Mr Healey complained would force him to make decisions that would “increase the risk to personnel on operations, and could make the country less safe”?
After the resignation he tweeted that Mr Healey had “given this country serious service in a serious time”. But he added that the threats facing the country “have not paused for a change of Secretary of State”, saying that the UK’s Armed Forces deserve a “Ministry of Defence that matches their seriousness with our own. That is the job. It continues today.”
In a sign of what may be to come were he to accept the job, he also said the defence investment plan, in its current form is “not fit for purpose”.
The security minister is a former member of the Parachute Regiment who served in the Balkans, Afghanistan and Iraq.
Mild mannered but deeply serious, he is sometimes likened to Mr Healey as an ultra-dependable minister.
He was once thought to have Labour leadership ambitions himself - and tipped as a challenger to Jeremy Corbyn when he led the Labour Party - but has kept a relatively low-profile in his current job.
His past service will make the defence secretary post attractive, but he faces the same question as Al Carns - can he accept a defence investment plan that Mr Healey has warned risks making the UK less safe?
Also a minister in the Ministry of Defence, he has been in charge of defence readiness and industry since last September.
A Plymouth MP and the son of a former Royal Navy submariner, he has an understanding of defence issues that could help steer the department through this turbulent time.
Heidi Alexander entered the cabinet last year after another resignation, that of the then transport secretary Louise Haigh over a decade-old conviction for wrongly telling the police her work mobile phone had been stolen.
Ms Alexander’s rise has been rapid. She only re-entered Parliament at the 2024 general election. Before that she had served as deputy Mayor of London for transport.
However, this is her second time in the Commons. During the first stint, as MP for Lewisham, she developed a reputation as a highly capable politician who was going places.
Just weeks ago she also denied she was planning to jump ship to support Mr Burnham and has, so far, stayed loyal to Sir Keir.
Widely seen as doing a good job in her current brief, she could be tapped up for a promotion.
