FACTBOX-British aviation security alerts
British police on Thursday said they had thwarted a plot to blow up planes in mid-flight between Britain and the United States and were holding 21 people.
The British Airports Authority said it had asked all European carriers to suspend flights to London's main Heathrow airport, where beefed-up security caused severe delays.
Here is a list of some recent British aviation security alerts:
December 22, 2001 - Airports around the world were on high alert after "shoe bomber" Richard Reid was caught apparently trying to blow up an American Airlines plane from Paris to Miami with explosives hidden in his shoes.