Just hours before her dramatic resignation, Dame Cressida Dick had been reassuring radio listeners that she was staying put as the head of the country’s largest police force. The Met commissioner, the first woman in the post, was determined to remain despite a succession of scandals and errors. Sadiq Khan, the Mayor of London, had been lukewarm in his support for the police chief but had not withdrawn it entirely.

That evidently changed yesterday, with Dame Cressida disclosing that she had “no choice” but to step down because the mayor had made it clear he had no confidence in her continuing in the job. It is apparent that the move took the Home Office by surprise. Mr Khan has said that he was not satisfied with her response to allegations of bullying and misogyny in the Met. But the mayor, who has been criticised for his poor record on crime, is already facing accusations that he squeezed Dame Cressida out for his own narrow political ends. It may even be that he overplayed his hand and he did not intend for her to resign in the first place.

Dame Cressida is the fourth commissioner in a row to leave under a cloud. Lord Blair was pushed out by Boris Johnson when he was mayor. Sir Paul Stephenson was caught up in the collateral damage inflicted by the newspaper hacking affair. Lord Hogan-Howe left early amid criticism over the Met’s handling of the disastrous Operation Midland investigation. The job has always been difficult because of its high profile and political sensitivity. But the loss of four successive commissioners in such circumstances suggests that it is a poisoned chalice for any potential replacement. Once the most coveted position in British policing, there will be many chief officers wondering whether it is worth applying. It also raises the question of whether the force is too unwieldy and needs to be split into different command structures.

The Met is not just responsible for crime fighting but for counter-terrorism and has the seat of government to protect as well. This means that the Home Secretary also has a role in the choice of commissioner. She and Mr Khan need now to agree on a successor. Recent incumbents have included the more cerebral like Lord Blair and the “copper’s copper” in the shape of Lord Hogan-Howe. Now the first woman in the job has stumbled. What qualifications are needed? Or might the force (or service as it prefers to style itself ) simply have become too big to be led effectively?