Chris Mason: What John Healey's resignation means

Two words leap out of John Healey's resignation letter and they amount to a devastating – and recurring – critique of Sir Keir Starmer's government.

The two words are "unwilling" and "unable".

"You have been unable and the Treasury has been unwilling to commit the resources that the nation needs to defend the country," he writes.

Healey is the sixth government minister to resign since Labour's disastrous showing in last month's elections.

He is the fourth full cabinet minister to resign from Sir Keir's government after Louise Haigh, Angela Rayner and Wes Streeting.

Healey's resignation as defence secretary comes on the day so many in Westminster expected would be when the government's long anticipated Defence Investment Plan was published.

It was becoming abundantly clear it wasn't going to see the light of day yet, because of rows within government about how to pay for it.

And this just a week before Healey was due to attend a Nato defence ministers meeting in Brussels - and a week before the crucial Makerfield by-election, when Andy Burnham could return to parliament and take on the prime minister.

Little wonder there was a desire from Sir Keir to get on with doing big stuff before then, if at all possible.

But now this. An already politically weakened prime minister weakened further.

We now know from Healey's resignation letter he saw the deal reached on Monday afternoon – with a view to it being published within a few days - and concluded it was nowhere near good enough.

The big picture is how does the government, or its successor, wrestle with the colossal trade offs that come with a desire for a massive increase in defence spending?

Where do cuts fall elsewhere, what does it mean for borrowing, what does it mean for taxes?

In the immediate moment, the prime minister, already drained of much authority, has to find a new defence secretary.

Who would want that job when the Defence Investment Plan is, politically speaking, a smoking mess – and when there could be a new prime minister within weeks or months?

And Sir Keir has to face up to the reality that yet another minister who has served in his government has departed with a broadside that amounts to deep-seated frustration as the inability of his administration to deliver what it promised it would.