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24 July 2010 Last updated at 11:30 GMT
Fighter jets from the Royal Air Force have taken part in a dramatic exercise to test Britain's readiness to respond to a terrorist hijack plot.
The pilots would be expected to shoot down a passenger plane if terrorists planned to crash it in a September 11-style attack.
The exercise involved two Eurofighter Typhoons, scrambled from an RAF base in the UK, tailing an airborne jet.
Home Secretary Theresa May is believed to have taken part in the exercise.
The security minister, Baroness Neville-Jones, was also among those who took part in the drill, in which fighter jets took off from RAF Coningsby, in Lincolnshire.
'Routine exercises'
The full-scale rehearsal, on July 8, was one of several counter terrorism exercises held each year in Britain to test readiness across government departments and the military.
The policy to shoot down a hijacked plane if it was considered a terror threat was introduced following the 2001 attacks in the US.
The pilots could be given an alternative: to damage the aircraft, for example by destroying an engine, forcing the plane to land.
The order to open fire on a packed passenger jet would be issued by a senior government figure.
A Home Office source said: "These are routine exercises and part of a national training programme."
Several British terrorists have been jailed for life in the past year for plotting to murder thousands of air passengers by detonating home-made liquid bombs on flights bound for major US cities.
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