The policeman who became the public face of the anti-terrorist effort is stepping down from his post, Scotland Yard announced yesterday.

Deputy Assistant Commissioner Peter Clarke, head of the Metropolitan Police’s Counter-terrorism Command, will retire by January 31 next year. Commander John McDowall, his deputy, is regarded as one of the front-runners to take his place but other officers will be considered. Under its equal opportunities recruitment policy, Scotland Yard will publicly advertise the £125,000-a-year post.

Mr Clarke has served 30 years in the Met. His successor will face unprecedented levels of al-Qaeda activity. Scotland Yard, MI5 and police national security units around the country are monitoring multiple suspected terror plots. The Times understands that there are 500 people in London alone whose activities are causing concern. Sir Ian Blair, the Met Commissioner, said that Mr Clarke had “performed outstandingly” in reshaping Scotland Yard’s anti-terror capability. Sir Ian added: “His contribution to the fight against terrorism has been truly significant.”

Mr Clarke, 52, is a father of three. He joined the Met in 1977 and was head of the Royalty Protection Squad in August 1997 when Diana, Princess of Wales, died in a car accident in Paris. He was heavily involved in the arrangements to return her body to Britain and in planning her funeral.

He rose to public prominence when he was appointed head of the antiterrorist branch in 2002 and set about transforming it from a unit concerned with IRA violence to one equipped to counter the global threat posed by al-Qaeda. Under his leadership the anti-terror squad was merged with Special Branch to form Counter-terrorism Command, or SO15, and working relations with MI5 were vastly improved.

Scotland Yard is now regarded as Europe’s lead force in counter-terrorist investigation and techniques.

In his role as national co-ordinator on anti-terrorist inquiries, Mr Clarke influenced major changes in the response to terrorism in police service across the country. Frustrated by widespread scepticism about the scale of the threat, he pioneered the approach of providing detailed information to the public in the wake of major incidents. He delivered measured statements after the July 7 bomb attacks and the attempted bombings of July 21. “I honestly believe,” he said in a speech this year, “that the safety of the British public will be secured as much by improving their understanding of the challenges we face as by any individual policy or piece of legislation.”

In the same speech Mr Clarke became one of the first to concede that al-Qaeda, far from being defeated, was resurgent and posing a direct threat to Britain. He said: “Al-Qaeda has been able to survive a prolonged multinational assault on its structures, personnel and logistics. It has certainly retained its ability to deliver centrally directed attacks here in the UK.”

Mr Clarke’s tenure as anti-terror chief is likely to be viewed as a success. The would-be suicide bombers of 21/7 were caught and were jailed for life earlier this year. Several major bomb plots have been thwarted and an increasing number of terror suspects are pleading guilty when faced with the weight of evidence against them.

Curriculum Vitae

Peter Clarke was born in 1955; he is married with three children

1977: graduates in law from Bristol University, joins Metropolitan Police
1984: promoted to rank of inspector at Tottenham; he is later made detective inspector while at Hackney
1993: staff officer to Sir Paul Condon, Met Commissioner
1994: appointed as Divisional Commander at Brixton
1996: promoted Commander in Specialist Operations Department at Scotland Yard.
1997: head of the Royalty and Diplomatic Protection squad
2000: deputy director of personnel for the Met
2002: assumed command of the Anti-Terrorist Branch, later Counter-terrorism Command.
2006: appointed OBE in New Year Honours list.

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