Well, Pan Am 103 wasn't a British plane, which is why it was Pan American and not Pan Brittanian, or whatever. It did depart Heathrow, however, 18 years ago, after a brief stopover. More importantly, Pan Am 103 originated in Frankfurt and that's certainly where the explosive cargo made it on board, to be where it was at. To be more precise, it was an unaccompanied suitcase routed automatically from an Air Malta flight to Pan Am 103 in Frankfurt.
Nowadays they are rewarded with 72 virgins for blowing up themselves along with passengers.