London  - Britain's top counter-terrorism officer resigned Thursday after his security blunder jeopardized a major anti-terror operation and triggered the premature arrest of 12 men suspected to have planned an imminent attack.

The men, including 10 Pakistani nationals who were in Britain on student visas, were suspected of having links with the al-Qaeda terrorism network and had been planning an imminent attack in Britain, reports said.

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

Quick resigned after he was pictured Wednesday clutching sensitive documents as he arrived in Downing Street to brief Prime Minister Gordon Brown and key ministers on the impending police operation.

Operation Pathway was planned to have been carried out in the early hours of Thursday, but was hastily brought forward because of the press photographs taken of the "top secret files."

As a result, 12 men suspected of links with the al-Qaeda terror network were arrested in the north-west of England, including in the cities of Manchester and Liverpool.

The majority were Thursday reported to be Pakistani nationals on student visas, and one Briton. They allegedly planned an imminent attack on a shopping centre or nightclub, reports said. dpa