If you lived in Northern Ireland, you'd be well used to seeing every policeman and woman carrying guns. But the idea of their presence being "reassuring" is a joke. What idiot thought that having a Scorpion tank at Heathrow could in any way be useful? If some bunch of maniacs parked a van bomb at the door of Terminal 1, I'd like to think they'd call the bomb squad rather than attack it with a Scorpion! Sometimes it would be comforting to know that they would have the wit not to use a sledgehammer to crack a nut! As for police provoking trouble, it has been widely reported in NI that the riot squad would often start trouble, because they got paid more if they were actually in a riot, than if they were just on standby. There is absolutely no doubt that on many occasions, the presence of police vehicles sparked off trouble.