Terror alert

Police officers guard London’s Stansted Airport.  (Cchris Radburn / AP)

Passengers wait at the check-in desks for their flights at Gatwick Airport in England.  (Tom Hevezi / AP)

British police officer guarding the Houses of Parliament in London, explains to a pass holder that she needs to go through a different entrance to the one she normally uses after Britain’s national security threat level was raised to critical.  (Matt Dunham / AP)

Airplanes wait on the tarmac after increased security measures were put into place at Manchester Airport in England.  (Jon Super / AP)

Passengers wait at the check-in for their flights at London’s Stansted Airport.  (Chris Radburn / AP)

Policemen are seen on duty at Manchester Airport after a terrorist plot to blow up aircraft in mid-air has been foiled by British police and security services in England.  (Peter Bryne / AP)

A passenger waits to check in for her flight to Toronto, Canada, with her plastic bag containing essentials. No standard hand baggage is permitted on any flights departing from Newcastle International Airport and other airports in England  (Scott Heppell / AP)