When they disintegrate, governments often do so slowly, then quickly. Despite dragooned public statements of support from the cabinet, the government of Keir Starmer gives every appearance of entering that second phase.

In the wake of the scandal surrounding former Washington ambassador Peter Mandelson and his ties to deceased sex offender Jeffrey Epstein, Starmer lost his chief of staff Morgan McSweeney, who had championed Mandelson for the role. Then the PM lost his press secretary, Tim Allan.

Then, in a live press conference, he lost the leader of the Scottish Labour party, Anas Sarwar. Eighteen months ago, Starmer could not have been closer to Sarwar. Now he has cut his national leader adrift and called for Starmer to resign.

Sarwar is not in Westminster. Sarwar has to fight an election in Scotland in May, and Starmer and the Westminster Labour government has been a liability for Scottish Labour for over a year. Sarwar had to act to have any chance of mounting a challenge against the governing Scottish National Party in those elections.

Sarwar’s actions may be be the most impactful, owing to the political momentum he has now so dramatically accelerated. But McSweeney’s resignation is the more significant development. The last line of defence for a prime minister is their chief of staff, and Sweeney was much more than that.

Party leaders and prime ministers have come not to be able to live without them, but so often are forced to. The chief of staff is part human, part metaphor: a conduit, a pressure valve, a lightning rod.

When forced out, their principal rarely lasts long, albeit as much for the related erosion........

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