Few people know that Britain has a class of nuclear bombs other than those carried in the Polaris submarines. Even their name was kept secret for 20 years. Now, without consulting Parliament, the Government has started work on a replacement. What Britain does next will have vital implications for our future defence and for relations with both Europe and America. For Panorama, Mark Urban , defence correspondent of the Independent, unravels the story of Britain's 'other' bomb. questions the military and political leaders involved in the decisions and the pilots who may have to bear the consequences.