The resignation of Andy Hayman leaves Britain’s anti-terrorist policing operation in crisis and reflects once more the turmoil at the top of Scotland Yard.

Assistant Commissioner Hayman was a popular figure with his officers and one who impressed the senior politicians and officials he briefed at times of emergency.

In partnership with Deputy Assistant Commissioner Peter Clarke he transformed the anti-terrorism apparatus in Britain.

Before 9/11 the old anti-terrorist branch was focussed solely on Irish republicanism. Today the Counterterrorism Command is a powerful, highly effective and pro-active arm of the police.

Mr Hayman could live with the criticisms of his unit as over-zealous and repressive. His aim, he maintained, was to make London and the UK a hostile environment in which terrorists would find it extremely difficult to operate.

Mr Clarke has postponed his retirement temporarily to fill the gap, but he too will be standing down in the New Year.

Who takes their places and what kind of anti-terrorist strategy will succeed them are certain to be interesting developments.

In recent months Mr Hayman had become disenchanted with the politics of policing - whether it was the endless debate about the future of Sir Ian Blair, the machinations at the Metropolitan Police Authority (MPA) or the criticisms from the Independent Police Complaints Commission (IPCC).

The IPCC singled him out in its Stockwell 2 report for not telling Sir Ian on July 22 2005 that Jean Charles de Menezes, shot dead by police that morning, was an innocent man. Mr Hayman was said to have briefed reporters that the wrong man had been killed, but not his commissioner.

The report led to a Peter Brookes cartoon in The Times depicting Sir Ian on parade with a ceremonial scapegoat on a lead. The goat was labelled AC Hayman.

Just 10 days ago, it was disclosed that Mr Hayman’s expenses had been scrutinised by police auditors and submitted to the MPA for further inquiries.

A former head of the Met’s anti-corruption unit, he robustly denied any impropriety and let it be known that he was thick-skinned and could take the flak.

But today he said that the “series of leaks and unfounded accusations” - including insinuations about a female staff officer - had been “very hurtful”. He had had enough.

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