Britain regularly sends up jet interceptors to practice chasing jet airliners and getting into position to shoot them down. This is usually kept quiet, but news of a recent exercise got out, and the government admitted that this was nothing new, but simply something the Royal Air Force has been regularly practicing for years.
The reason for these drills is the large number of Islamic terrorists in Britain who have been caught trying to carry out attacks on airliners. Most of these involve setting off explosives while the aircraft is in the air. But some terrorist groups have studied the possibility of taking over airliners and crashing them into "high value targets" (like Parliament, Buckingham Palace or London's financial district). For this eventuality, the Royal Air Force trains to prevent the terrorists from using a hijacked airliner as a guided missile.