RAF fighters were scrambled 200 times a year to intercept unidentified targets on the radar of Britain's air defence systems during the cold war right up until 1991, according to the latest batch of UFO files releasedby the National Archives today.

In the majority of these cases the mystery flying object penetrating Britain's defences turned out to be a Soviet long-range reconnaissance or anti-submarine aircraft. According to a background note in an MoD file the last RAF fighter jet to be scrambled to investigate such a UFO took off in September 1991 in the immediate aftermath of the break-up of the Soviet Union.

But as the 18 sets of files released today – the sixth batch so far -show that while no RAF scrambles were recorded in the five years between 1991 and 1996, the public submitted more than 1,200 reports of sightings of UFOs.

prime minister Winston Churchill ordered a UFO sighting be kept secret to prevent "mass panic".