Police arrested 12 men in counter-terrorism raids across northwest England on Wednesday hours after a security blunder by a top police officer. The afternoon raids involving several hundred officers took place after Britain's most senior counter-terrorism officer was photographed openly carrying a secret document detailing plans for the arrests. Media said the raids were brought forward because of the potential security breach by Scotland Yard's Assistant Commissioner Bob Quick. The document, headlined "Briefing Note: Operation Pathway" described the operation as a "Security Service-led investigation into suspected AQ (al Qaeda) driven attack planning within the UK." It said 11 people were targeted for arrest, 10 of them Pakistan nationals in Britain on student visas, and one British. Quick was photographed with the document, labeled "secret," outside Prime Minister Gordon Brown's Downing Street offices in London. "Assistant Commissioner Quick accepts he made a mistake in leaving sensitive documents on open view," Scotland Yard said. "He deeply regrets it and has apologized to the commissioner and colleagues." The opposition Conservatives said Quick had made an "extraordinary and very alarming lapse." "It will lead to serious questions about his judgment and about his ability to do his job properly," said Conservative Home Affairs spokesman Chris Grayling. Home Secretary Jacqui Smith congratulated police on conducting a successful anti-terrorism operation, adding that Britain faced a "severe terrorist threat." "The decision to take such action was an operational matter for the police and the security service but the prime minister and I were kept fully appraised of developments," she said. Detective Chief Superintendent Tony Porter, head of the North West Counter-Terrorism Unit, said the raids were part of a continuing operation and that police had acted on intelligence received. Officers searched eight addresses in Manchester, Liverpool and Lancashire and arrested the 12 men at seven different places. One was held at Liverpool's John Moores University, two at a home improvements store in Clitheroe, Lancashire, and one on a motorway in Manchester. Four others were held in Liverpool and four in Manchester. The arrested men ranged from a teenager to a 41-year-old man, police said.