A passenger jet coming in to land at Heathrow Airport had a near miss with a UFO, newly-released Ministry of Defence files reveal today.

The captain of the Alitalia airliner was so concerned he shouted “look out” to his co-pilot after seeing a brown missile-shaped object shoot past them overhead.

The mysterious incident near Lydd in Kent in 1991 was thoroughly investigated by the Civil Aviation Authority (CAA) and the military.

But having ruled out the object being a missile, weather balloon or space rocket, the MoD closed the inquiry and left the matter unsolved.

The unexplained close encounter is one of many recounted in military UFO documents made available online today by the National Archives.

Covering sightings from between 1986 and 1992, the 19 files include:

• a US Air Force pilot’s account of being ordered to shoot down a UFO that appeared on his radar while he flew over East Anglia;
• an MoD request that Army and Navy helicopters should not take photographs of crop circles for fear of undermining the official line that the military did not investigate unexplained phenomena;
• a letter from a woman claiming to be from the Sirius system who said her spacecraft — also containing two “Spectrans” with “Mr Spock ears” — crashed in Britain during the Second World War.

But one of the most intriguing episodes is the near-miss involving the Alitalia airliner at about 8pm on April 21 1991.

The McDonnell Douglas MD80 aircraft was en route from Milan to Heathrow at 22,000ft with 57 people on board when pilot Achille Zaghetti saw the strange object some 1,000ft above him.

He recounted: “At once I said, ‘Look out, look out,’ to my co-pilot, who looked out and saw what I had seen.

“As soon as the object crossed us I asked to the ACC (area control centre) operator if he saw something on his screen and he answered, ‘I see an unknown target 10nm (nautical miles) behind you’.”

A CAA document notes that Southern TV broadcast a story about a 14-year-old boy who reported seeing a missile flying at low level before climbing through the cloud and disappearing on the same evening.

Radar images showing the UFO were initial labelled “cruise missile??” but it was quickly established that it was not a military weapon.

^{An Alitalia pilot’s report on the 1991 ‘near miss’}

By July 2 the MoD had concluded that the object had not come from the Army firing ranges in the Lydd area and that there was no known “space-related activity” that night.

An unnamed Whitehall official wrote: “It is our intention to treat this sighting like that of any other Unidentified Flying Object and therefore we will not be undertaking any further investigation.”

There were, however, a number of other similar incidents recorded the same year.

The files can be accessed at www.nationalarchives.gov.uk/ufos