Sir Winston Churchill was accused of covering up a close encounter between an RAF aircraft and a UFO during the World War II, newly-released files revealed yesterday.

The former Prime Minister allegedly ordered that the unexplained incident over the east coast of England should be kept secret for at least 50 years because it would provoke “mass panic”.

The claim, made by a scientist who said his grandfather was one of Sir Winston’s bodyguards, is recounted in declassified Ministry of Defence UFO files made available online by the National Archives.

Allegations of the cover-up emerged when the man, from Leicester, wrote to the government in 1999 seeking to find out more about the incident.

He described how his grandfather, who served with the RAF in the war, was present when Sir Winston and US General Dwight Eisenhower discussed how to deal with the UFO encounter.

The man, who is not named in the files, said Sir Winston was reported to have exclaimed: “This event should be immediately classified since it would create mass panic among the general population and destroy one’s belief in the Church.” The incident allegedly involved an RAF reconnaissance plane returning from a mission in France or Germany towards the end of the war.

It was over or near the English coastline when it was suddenly intercepted by a strange metallic object which matched the aircraft’s course and speed for a time before accelerating away and disappearing.

The scientist said: “This event was discussed by Sir Winston and General Eisenhower, neither of whom knew what had been observed.

“There was a general inability for either side to match a plausible account to these observations, and this caused a high degree of concern.”

Whitehall officials investigated the claims but could find no records of the discussions between Sir Winston and Gen. Eisenhower, the newly-released documents show.

An MoD official wrote back to the man in September 1999: “It was generally the case that before 1967 all UFO files were destroyed after five years as there was insufficient public interest in the subject to merit their permanent retention.

“Therefore, any UFO report files from the World War II era would most probably have been destroyed.”

And a month later a civil servant in the Cabinet Office told him: “In your letter, you say that the discussion between Sir Winston and Gen. Eisenhower on the UFO sighting should have been recorded.

“We have had a look through our lists of material for this period, and I am afraid that we cannot immediately see anything on this subject. Neither do we have any filed on this matter which remain closed.” Sir Winston is known to have expressed an interest in UFOs. He wrote to his ministers in July 1952: “What does all this stuff about flying saucers amount to? What can it mean? What is the truth? Let me have a report at your convenience.”

Other incidents recorded in the 18 MoD files released yesterday, which cover the years 1995 to 2003, include:

• A man who went to RAF Stanmore in north London to warn military police he had dreamed that a bomb would explode in London in the “near future”. About eight to nine weeks later, in May 1990, RAF Stanmore was targeted by a terrorist bombing.

• A gambler who appealed for the government’s help after Ladbrokes refused to pay out on his 100-1 bet that aliens would land on earth before the end of the 20th century.

• The famous 1974 UFO sighting over the Berwyn Mountains in north Wales, which officials concluded could be explained by a combination of an earthquake and a meteor.

• Details of how the UK’s Joint Intelligence Committee discussed UFOs in 1957 and was told that some unusual radar readings remained unexplained.

• A memo revealing that RAF jets were scrambled to investigate unexpected objects picked up on radar 200 times a year during the Cold War – but that this fell to zero after the collapse of the Soviet Union in 1991.

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