In order to prevent a mass panic, Winston Churchill kept top secret a close encounter between a World War II pilot and an unexplained flying object, newly unclassified documents
reveal.

http://www.foxnews.com/scitech/2010/08/05/churchill-ordered-ufo-cover-up/?test=latestnews

Same Subject just another Link:

British X-Files describe secret UFO encounters
By Maria Golovnina, Reuters

LONDON - Britain released hundreds of previously secret “UFO files” on Thursday including a letter saying that Winston Churchill had ordered a 50 year cover-up of a wartime encounter between a UFO and military pilot.

The files, published by the National Archives, span decades and contain scores of witness accounts, sketches and classified briefing notes documenting mysterious sightings across Britain.

http://cnews.canoe.ca/CNEWS/World/2010/08/05/14929131.html