LONDON - Britain's top counter-terrorism officer announced his resignation on Tuesday, after criticism following the police shooting of a Brazilian man mistaken for a suicide bomber and reports of a probe into his expenses.

Assistant Commissioner Andy Hayman, who headed the Metropolitan Police's Specialist Operations unit which includes the Counter Terrorism Command, said he was quitting the post with immediate effect and retiring from the force.

"This role requires total commitment in both time and effort and has a considerable impact on your personal life, your family and friends," said Hayman, 47, who took over the role in February 2005.

"It also puts you in the spotlight, often in ways that are very hurtful. Recent weeks have seen a series of leaks and unfounded accusations about me, which I have and will continue to refute strongly."

Hayman was referring to media reports which said he was being investigated over expenses claims and foreign trips with a woman police sergeant.

In August, a report by the Independent Police Complaints Commission (IPCC) condemned Hayman for his behaviour in the aftermath of the shooting of Jean Charles de Menezes who was killed by police on an underground train in July 2005.

The watchdog said Hayman had misled other officers by not telling them the dead man was innocent. This led to false information being given to the press and the public, the IPCC decided, voicing "serious concern" over his actions.

Hayman had become a well-known public figure in the aftermath of the deadly July 7, 2005 London bombings, often fronting live TV news conferences giving regular updates on how the police investigation was progressing.

However, he came in for criticism the following year over a dramatic anti-terrorism raid on a house in east London in which a man was shot.

Hayman said officers had been acting on intelligence that the house was being used to make a chemical bomb, but no such device was found and the wounded man, and his brother, who were arrested in the raid, were later released without charge.

"Andy Hayman can be very proud of the achievements and successes during his time in charge of Specialist Operations," said London's police chief Ian Blair, who himself has faced calls to resign over the de Menezes shooting.

"In this year alone, 37 people have been convicted in terrorist-related cases following investigation by the Met."

Peter Clarke, current head of the national Counter Terrorism Command, has postponed his own retirement to take on Hayman's role on a temporary basis until a replacement is chosen.