Over 1,000 pages of government reports on UFO activity in Britain were revealed yesterday at the National Archives in Kew. They clearly indicate several famous sightings in the early 1990s were never solved.

The opening of this treasure trove of information on UFOs comes during an increase in reports of UFO sightings in England, including this one pictured above, snapped over London last week. The newly-declassified government reports cover UFOs reported between 1987 and 1993. While many of the sightings were proven to be caused by natural (or human-generated) phenomena, one incident in particular frightened the government a great deal and has never been solved.

This incident took place in 1990 over Scotland, where many witnesses spotted diamond-shaped ships [pictured] as well as military jets. According to The Telegraph:

The Ministry of Defence first became aware of the existence of the craft when the Daily Record newspaper presented it with six colour photographs of the object. The UFO seen by two men, one of whom captured it on camera, as it hovered in daylight near the A9, at Calvine, north of Pitlochry, on August 4, 1990.

The witnesses said it hovered for about 10 minutes – during which time military aircraft were also seen making a series of low-level passes – before moving upwards, out of sight, at great speed.

The files show that officials established from the photographs that the military craft were Harrier jets even though, intriguingly, none were operational in the area at the time.

An MoD minute prepared for the then Armed Forces Minister, Sir Archie Hamilton, and dated September 14, 1990 states: . . . "They [the photographs] show a large stationary, diamond-shaped object past which, it appears, a small jet aircraft is flying. The negatives have been considered by the relevant staff who have established that the jet aircraft is a Harrier (and also identified a barely visible second aircraft, again probably a Harrier) but have reached no definite conclusion regarding the large object." . . . The files show that a year after the original photographs were taken, the MoD tasked experts to produce line drawings of the UFO which would give officials an idea of scale.

Even the creation of the drawings was shrouded in strict secrecy. One undated document suggests "very special handling" because of "sensitivity of the material". It also orders "minimum handling by listed personnel".

The papers also include dozens of other unsolved reports that are definitely worthy of X-Files. Here's my favorite:

March 31, 1993: More than 100 people in the West Country and Ireland report seeing two brilliant objects with bright vapour trails flying North to South quickly and silently across the night sky - an episode now known to Ufologists as the Cosford Incident. Officials say some of the sightings may have a been a Russian Cosmos satellite re-entering Earth's atmosphere, but cannot explain away the sightings entirely. An official notes: "Personally I agree that while the decay of Cosmos 2238 might explain the high level 1.10am sightings, it would not explain the other sightings in the night in question."

As for all the UFO sightings in England right now, though, we all know it's that fly-headed alien in coveralls from the next Doctor Who special coming up.

Learn more about the British government's obsession with UFOs in The Telegraph.