ONE of al-Qaeda’s most dangerous figures has been revealed as a double agent working for MI5, raising criticism from European governments, which repeatedly called for his arrest. Britain ignored warnings — which began before the September 11 attacks — from half a dozen friendly governments about Abu Qatada’s links with terrorist groups and refused to arrest him. Intelligence chiefs hid from European allies their intention to use the cleric as a key informer against Islamic militants in Britain. Abu Qatada boasted to MI5 that he could prevent terrorist attacks and offered to expose dangerous extremists, while all along he was...