Britain's most famous UFO mystery was a prank played on the Americans by the SAS, according to insiders.

The truth about the Rendlesham Forest incident in Suffolk has been kept under wraps for 38 years. But now it is claimed the US air force was fooled by the SAS in revenge for capturing a squad and subjecting them to a brutal interrogation.

The SAS were said to have regularly tested US security by probing the perimeters of RAF Woodbridge in Suffolk. Nuclear warheads were said to be stored there and it was believed to be a key target for Soviet agents. But when an SAS troop parachuted into the complex one night in August 1980 they were unaware the guards had upgraded their radar system.

Their black parachutes were immediately detected and the British were hauled off for questioning. They claimed they were beaten up by their captors who refused to believe who they were and repeatedly referred to as “unidentified aliens”.

They were eventually released 18 hours later after the British authorities intervened. But the SAS soldiers were seething at being called aliens on their own soil and reportedly started plotting their revenge.