There's an old saying that the best place to hide a book is in a library. The latest Ministry of Defence UFO files released to the National Archives contain more than 6,000 pages of documentation, so if there was a memo somewhere in there saying the MoD had a crashed spaceship hidden away in an RAF hangar somewhere, it might not be found.

Before I start all manner of conspiracy theories with that remark, however, I should say that there is no such memo and no such spaceship – and I say that as someone who spent three years of my 21-year MoD career working on this issue.

This is the fifth batch of UFO files to be made available and is part of an ongoing three-year programme to release the entire archive. The decision to release the files was taken in 2007, to deal with the administrative burden of responding to requests made under the Freedom of Information Act. At one time, MoD was receiving more FOI requests on UFOs than on any other subject.

The newly released files cover the period 1994 to 2000. It's interesting to note that the cult TV series The X-Files was at the height of its popularity at this time. Might this have influenced people making UFO reports?

I'm sceptical about the link between science fiction and UFO sightings. While the popularity of The X-Files might make some people speculate about aliens and government cover-ups, there's no evidence to suggest that sci-fi films and TV shows influence people's perceptions of anything strange that they see. Given the current stratospheric popularity of the blockbuster movie Avatar, if people were being influenced by sci-fi in the way suggested, we'd be inundated with reports of people seeing blue aliens. We're not!

So, how do the MoD's real-life Mulders and Scullys compare to their fictional counterparts? Having done the job myself, from 1991 to 1994, I'm sorry to have to report that it's not quite as glamorous as people might suspect. There's no running around dark warehouses with guns and torches. It's more a case of asking colleagues in the RAF to check the radar tapes and writing polite letters back to members of the public, stating that most UFOs turn out to be misidentifications of ordinary objects and phenomena.

For those with the patience to wade through 6,000 pages of documents, it's a mixed bag. There's a great deal of mundane correspondence between the MoD and the public, together with a vast number of UFO sightings which are clearly aircraft lights, satellites or meteors. But there is some more interesting material.

As well as today's news story regarding the sighting of a large, triangular "humming" object in the sky above Michael Howard's Folkestone home, other examples include the UFO seen by a police officer over the ground of Chelsea FC, and the air traffic controller at Prestwick who tracked an uncorrelated target on radar, travelling at phenomenal speed. Most disturbing, however, is the incident that occurred on 6 January 1995, when a Boeing 737 on approach to Manchester airport nearly collided with a delta-shaped UFO. The pilot and first officer both witnessed this and made an official report. Neither the MoD nor the Civil Aviation Authority could find any explanation.

As one reads the files, one can sense the MoD's growing irritation with the subject – an irritation that arguably culminated on 1 December 2009 when the MoD finally disengaged altogether and announced that they would no longer be investigating UFO sightings reported by the public. Some of the files are entitled "persistent correspondent". This is a coded way of saying "this person is becoming a nuisance". As will be seen in future file releases – the last files won't be released until 2011 – this frustration boiled over when the Freedom of Information Act came fully into force.

Another sign of the MoD's "corporate irritation" with the subject is revealed in the response to somebody who claimed to have been kidnapped by aliens (it's not just UFOs; these real-life X-Files include material on other mysteries such as alien abductions and crop circles). The person concerned had written to ask about MoD policy on alien abductions and pointed out that if the experience was real, the MoD was failing to maintain the territorial integrity of UK airspace – a core defence mission. After explaining the MoD's role with respect to UFOs, the somewhat sniffy response stated: "Abduction is a criminal offence and as such is a matter for the civil police."

This conjures up the bizarre thought of a flying saucer landed on the side of a road, with a bemused constable leaning through the entrance hatch saying, "Excuse me sir, have you any idea how fast you were going?"