Britain's top anti-terror officer was forced out because of a “dirty tricks” campaign by disgruntled police officers, it was claimed last night .

Britain's top anti-terror officer was forced out because of a "dirty-tricks" campaign by disgruntled officers, it was claimed last night.

The Met's assistant commissioner Andy Hayman - Norfolk's chief constable from December 2002 to February 2005 - announced his decision to retire on Tuesday. Mr Hayman was facing an inquiry into expenses claims and allegations that he had "inappropriate contact" with a woman official at the Independent Police Complaints Commission.

Mr Hayman, 48, is said to have exchanged more than 400 phone calls and texts with the employee while the IPCC was writing a report into the Met's handling of the shooting of Jean Charles de Menezes at Stockwell in 2005.

The anti-terror chief, who was in overall charge of London's security at the time, was later criticised in reports on the incident.

The latest accusations in a Channel 4 News bulletin follow an earlier revelation that auditors were investigating his £15,000 expense claims and questions over business trips abroad with one of his officers, Heidi Tubby, a former Norfolk police officer.

Mr Hayman announced his early retirement and hit out at "unfounded accusations".

Channel 4 said the latest claims called into question the integrity and independence of the IPCC's report into the Stockwell shooting. However, the IPCC announced that the official had no inside knowledge of the de Menezes report. In a statement, the IPCC said the woman was not an investigator and had no involvement or contact with the IPCC's two Stockwell inquiries. It said: "We have satisfied ourselves that there was no improper sharing of information. It appears that the calls were not work-related."

Mr Hayman's resignation provoked disbelief and fury at Scotland Yard. Sir Ian is facing continuing pressure over his leadership with calls from Tory and Lib Dem politicians to resign over the de Menezes shooting. One of Mr Hayman's colleagues claimed he had been the victim of a "dirty-tricks campaign" and there were claims he was being made a "scapegoat" to divert attention from the commissioner.

He said Mr Hayman had always kept in touch with the friend at the IPCC and the fact that she worked at the police watchdog at the time was coincidental. He said: "You have to remember that Andy has driven through a lot of change and shaken up a lot of cosy gentlemen's clubs within Special Branch. He has annoyed a lot of people. Andy has answers to all these accusations but there is only so much you can take. He ended up with an ultimatum from home. He has chosen his family."

Another source close to the Met said: "Ian Blair is in a position where his senior management team is unravelling around him... This does not reflect very well on his leadership abilities."