An independent public inquiry should be held into how suicide terrorists were able to carry out the July 7 bombings, Scotland Yard’s former head of counter-terrorism says.

Andy Hayman, who was Assistant Commissioner for Special Operations at the time of the bombings in 2005, is the first figure from the security establishment to break ranks and call for an open inquiry.

Almost four years after Mohammad Sidique Khan and his Leeds-based cell carried out the bombings, Mr Hayman says that he is “uncomfortable” with the official position that an inquiry would divert resources from the fight against terrorism. In his book, The Terrorist Hunters, extracts from which are published in The Times today, Mr Hayman says: “Incidents of less gravity have attracted the status of a public inquiry — train crashes, a death in custody, and even other terrorist attacks. How can there not be a full, independent public inquiry into the deaths of 52 commuters on London’s transport system?

“There has been no overview, no pulling together of each strand of review, no one can be sure if key issues have been missed.”

Survivors of the July 7 bombings and families of the victims are taking High Court action over the refusal to grant them an independent inquiry.

The key issue for any inquiry would be why Khan, 30, who had been photographed, followed and bugged by surveillance officers because of his links with known terrorists, was left free to carry out the attacks.

A report last month by the parliamentary Intelligence and Security Committee (ISC) said that MI5’s decision not to make Khan a priority target was “understandable and reasonable”. But that report, prepared by a committee that was appointed by the Prime Minister and took evidence in secret, has been heavily criticised.

It reveals that one MI5 team had begun an operation to identify a suspect known as “Ibrahim”, who was later revealed to be Khan. At the same time, others in MI5 knew where Khan lived but had decided that he was not a key suspect. Critics say that the ISC does not appear to have inquired how the mismatch happened.

In his book, Mr Hayman paints a vivid picture from inside Scotland Yard of the day the bombers struck and admits that the attacks were “a bolt from nowhere”.

He was called to a meeting of Cobra, the Government’s emergency meeting, within an hour of the first explosions, and had to admit that he did not know what was happening.

Mr Hayman writes: “Imagine what it’s like to tell the Commissioner or the Secretary of State, as I would have to, ‘I don’t know what’s going on’.”

Rachel North, a survivor of the Piccadilly Line bomb at King’s Cross, welcomed his support for an inquiry. “It is not to blame or have a witch-hunt but. . . to learn the lessons of how 7/7 happened and whether it could have been prevented.”

• Sir Ian Blair, who as commissioner of the Metropolitan Police was in charge at the time of the London bombings, has received a substantial payoff. He was paid £580,000 during his final eight months in office, more than doubling his annual salary, and stands to benefit from a pension pot of £3.5 million.

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