BRITAIN'S top counter-terrorism officer today said he "deeply regretted" jeopardising a major operation after resigning from his post.

Assistant Commissioner Bob Quick quit his top Scotland Yard role today after being pictured carrying secret documents into 10 Downing Street.

Mr Quick, a former chief constable of Surrey, said: "Last evening I contacted the Metropolitan Police Authority to inform them of my intention to offer my resignation.

"I have today offered my resignation in the knowledge my action could have compromised a major counter-terrorism operation.

"I deeply regret the disruption caused to colleagues undertaking the operation and remain grateful for the way in which they adapted quickly and professionally to a revised timescale."

Met Commissioner Sir Paul Stephenson paid tribute to Mr Quick as it emerged Assistant Commissioner John Yates will take charge of the force's specialist operations wing.

Sir Paul said: "Bob Quick is a tremendous police officer who has served with dedication and professionalism throughout his career.

"I hold Bob in the highest regard, as a friend and colleague, and that opinion has not changed. He has accepted that he made a serious error and that has led to his resignation.

"I would like to thank Bob for the excellent job he has done leading the national response to the terrorist threat and the way in which he has led the counter-terrorist command in London.

"It is important in such a critical policing role to announce Bob's successor. I have today appointed Assistant Commissioner John Yates as head of specialist operations."

Mr Quick's downfall came after he was pictured yesterday clutching sensitive documents as he arrived for a meeting with the Prime Minister and the Home Secretary.

The documents showed top-secret details of a major anti-terror operation in north west England and meant a police operation to arrest the suspects had to be brought forward.

After the blunder, the Defence Press and Broadcasting Advisory Committee, which advises the media of issues of national security, issued a request to news organisations not to print the photographs of Mr Quick showing the details of the operation.

But fearing suspects would be tipped off about the operation, police swooped yesterday afternoon on addresses in Manchester, Liverpool - including John Moores University - and Clitheroe, in Lancashire.

A Homebase store in Clitheroe was also raided by more than 100 officers. Two staff members, thought to be security guards, were arrested.

Security sources said the group were feared to have links with a known al Qaida suspect in Pakistan and had been under surveillance by police and MI5.

Searches were continuing at addresses in the North West today after hundreds of officers carried out the raids on 10 properties and arrested 12 men - including 10 Pakistani nationals on student visas and one Briton.

London Mayor Boris Johnson said he had accepted Assistant Commissioner Bob Quick's resignation with "great reluctance and sadness".

He said: "It is with deep regret that I accepted the resignation of AC Bob Quick. Bob understands fully the security breach which occurred yesterday was a serious issue for which he has taken personal responsibility."

Home Secretary Jacqui Smith said Mr Quick felt his position was "untenable" following the publication of the photographs and thanked him for his work.

She said: "I want to offer my sincere appreciation for all the outstanding work he has done in this role which has helped keep this country safe." Quick was no stranger to hitting the headlines

AS Britain's most senior counter terrorism police officer, Assistant Commissioner Bob Quick was no stranger to controversy.

The head of Scotland Yard's specialist operations wing returned to the Metropolitan Police last year from Surrey where he was chief constable.

In December he apologised for an outburst in which he accused senior Tories of leaking a story about his wife's business interests.

Mr Quick faced unwanted newspaper headlines after it emerged his wife Judith was running a luxury car hire firm from their home and details of their address were published on a website.

The stories followed hot on the heels of his involvement in overseeing the arrest of Shadow Immigration Minister Damian Green as part of a Whitehall leak inquiry.

Speaking at his home, Mr Quick, a father of five, told a reporter his wife and children were forced to move out because of security concerns sparked by the row.

The comments were an unusual response from a man who regularly met members of the global intelligence community and whose role thrived on discretion.

An Exeter and Cambridge universities graduate, Mr Quick joined the Metropolitan Police in 1978, serving in Lambeth.

He moved quickly through the ranks, training as a detective and investigating murders and other serious violent crimes, being posted to Brixton in 1982.

At one time he led Scotland Yard's anti-corruption unit, a role reserved for officers whose reputations are spotless.

Mr Quick, a commander at the time, was widely praised in 2002 for the restraint shown by police during what was London's longest armed siege. It ended after 15 days when the gunman, Eli Hall, shot himself, before fire took hold of the flat. No one else was hurt.

In 2003 he transferred to Surrey Police to become the force's deputy chief constable and the following year was appointed chief constable.

After being appointed to his terrorism role, Mr Quick was responsible for co-ordinating work to disrupt and prevent terrorist attacks in Britain.

He had focused on improving communications between residents and police in neighbourhoods where extremism may flourish.

Now a new man will have to carry on the job.