Britain's top counter-terror police officer resigned Thursday after his security blunder led to a major swoop on suspects being hastily brought forward. Assistant Metropolitan Police Commissioner Bob Quick tendered his resignation to London Mayor Boris Johnson following Wednesday's intelligence gaffe. Quick said he deeply regretted the disruption caused to colleagues when he inadvertently revealed details of a counter-terrorism operation. He was photographed as he arrived at Prime Minister Gordon Brown's Downing Street office for talks on police reform with a sensitive document clearly visible. It contained details about a planned operation, including that there were 11 suspects -- 10 of them of Pakistani origin and in Britain on student visas, and one British born -- and where the raids would take place. Police arrested 12 people under the Terrorism Act in evening raids Wednesday across northwest England, which media reports said had been planned for Thursday morning but were hastily rescheduled.