Andy Hayman, Britain's top anti-terror copy - and previously a senior officer in Norfolk and Essex - is to retire after allegations of expense irregularities.

The man in charge of Britain's fight against terrorism is to step down just days after the launch of an investigation in to his expense claims.

Assistant commissioner Andy Hayman - who was chief constable of Norfolk police before taking up the role - said the “time was right” to leave the Met.

“Recent weeks have seen a series of leaks and unfounded accusations about me, which I have and will continue to refute strongly,” he said.

Last week it emerged that Mr Hayman was facing an investigation into his expenses claims and foreign trips with a woman police sergeant, after the Metropolitan Police Authority confirmed that a report was being prepared for consideration by the force's professional standards subcommittee.

It is believed Mr Hayman was being quizzed about £15,000 in expenses including claims for large amounts of alcohol and entertaining.

He has also been asked about his relationship with Sergeant Heidi Tubby, his former staff officer, who is said to have accompanied him on foreign business trips at public expense.

She worked as Hayman's staff officer when he was chief constable of Norfolk police and followed Hayman to London in 2005.

He has also separately faced criticism for his actions in the aftermath of the shooting of Jean Charles de Menezes by Met officers at Stockwell tube station.

Mr Hayman's police career started in Essex in 1978, and he first joined the Met in 1998 as commander.

From 1999 he headed up the Met's anti-corruption department, moving to Norfolk Constabulary in December 2002.

He re-joined the Met from Norfolk in February 2005 after serving just over two years at the force as chief constable.

His recent duties at the Met included leading the fight against Islamist terrorism and protecting the Royal family.

In a statement on his retirement he said: “It has been a great honour and privilege to lead Specialist Operations in its challenging work protecting this country from the palpable terrorist threat we face.

“This role requires total commitment in both time and effort and has a considerable impact on your personal life, your family and friends. 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.

“However, these events take their toll on you personally and I feel now is the right time for me to step aside and for a new person to take over as Assistant Commissioner Specialist Operations and Head of the ACPO Terrorism and Allied Matters business area. I wish my successor and all my colleagues every success in their continued efforts to defend the United Kingdom.”

Mr Hayman was backed by Metropolitan Police commissioner, Sir Ian Blair, who himself has faced calls to quit in recent months.

“Andy Hayman can be very proud of the achievements and successes during his time in charge of Specialist Operations,” he said.

“In this year alone, 37 people have been convicted in terrorist related cases following investigation by the Met. He has also made a significant contribution to the development of policing and the service during his career. I fully understand his decision to leave at this time and wish him well for the future.”

As well as his police roles, Mr Hayman is on the board of governors of Anglia Polytechnic University and is an external examiner for Cambridge University.