A dead man walking: Willie Carlin - MI5's top spy inside Sinn Fein

A self-confessed republican informer, who calls himself "Margaret Thatcher's spy" and who infiltrated Sinn Fein to get close to Martin McGuinness, says he still fears he'll be murdered - more than 30 years after he was spirited out of Londonderry on the Prime Minister's private jet when his cover was blown.