Keir Starmer's Downing Street is in fresh crisis this morning after a second very senior aide quit in the space of just 24 hours.  The PM's head of communications, Tim Allan, has said he is leaving to "allow a new No. 10 team to be built". It's the Prime Minister's fourth Chief of Communications in just 18 months, suggesting mass instability.

It comes just a day after Morgan McSweeney, Sir Keir's chief of staff, quit yesterday over his role in the appointment of Peter Mandelson as US ambassador. Allan followed a line of departed heads of communications in Sir Keir's No. 10 operation, after Matthew Doyle, James Lyons, and Steph Driver.

Mr Allan's resignation statement in full read: "I have decided to stand down to allow a new No10 team to be built. I wish the PM and his team every success.”

It's not known precisely why Mr Allan has gone, though many in government perceived him to be ineffective at his job.

The latest departure suggests a Downing Street in all-out chaos and freefall.

Morgan McSweeney quit yesterday, citing his role in the appointment of Peter Mandelson to the top diplomatic posting in Washington. In his resignation statement, Mr McSweeney said: "The decision to appoint Peter Mandelson was wrong. He has damaged our party, our country and trust in politics itself.

"When asked, I advised the prime minister to make that appointment and I take full responsibility for that advice. In public life responsibility must be owned when it matters most, not just when it is most convenient. In the circumstances, the only honourable course is to step aside."

No. 10 has insisted that Keir Starmer will not be making any public statements today, explicitly ruling out a "lectern moment" outside the black Downing Street door in which he would be expected to resign.

His main event for the day will be a furious showdown at a meeting of the Parliamentary Labour Party this evening, which could seal his fate if it goes badly.

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