Conspiracy theorists expecting to find that the Ministry of Defence has been sitting on some great truth about visiting extraterrestrials will be hugely disappointed.

There are no aliens in these files — at least, not aside from what might charitably be called letters from people with overactive imaginations. Most of the contents of the MoD's newly released UFO files are mundane and are clearly misidentifications of ordinary objects and phenomena.

This should not be taken as an indication that these people are stupid and, indeed, in among the reports from members of the public are sightings from police officers, pilots and military personnel.

Arguably the most interesting thing in the files is what they show overall, namely that since the 1950s the Ministry of Defence has tracked UFO sightings, investigated the sighting and searched its collective soul over what to make of this enigmatic mystery.

But why should this be the case? Why, since records began, has the MoD spent time and money looking at UFOs? The answer has more to do with Russians than Martians. The MoD and the RAF naturally keep a close watch on the UK's air defence region, ever-watchful for signs of intrusion. If there is something in our skies and it is not ours, we want to know whose it is. I worked for the MoD for 21 years and, during the early 90s, worked in a division where my duties included investigating UFO sightings.

My brief wasn't to look for aliens, but to look for evidence of anything of any defence significance - though, interestingly, this term was never defined. I started my tour of duty as a sceptic but, after three years of research and investigation, felt that while I hadn't found ET, I had come across some cases that made me think twice. UFOs tracked on radar or seen by military witnesses were particularly interesting to me.

This file release will not resolve the UFO mystery one way or the other. Sceptics and believers alike will doubtless find something to back up their case. But what strikes me is the enduring power of UFOs to fascinate the imagination.

UFOs burst upon the scene in the late 1940s and early 1950s. They are still here. The debate goes on. Perhaps it is the implications if - among these tens of thousands of reports - just one of them turned out to be the real thing.

The question of whether or not we are alone in the Universe is among the most profound questions that we can ask. The answer to that question is not in these files. But they do show that people are still looking up, watching and wondering.

Nick Pope ran the MoD's UFO desk from 1991-94

Times Recommends

• An officer and a gentle woman
• Dame Helen Mirren is worthy of the Epidaurus
• Foods that can help to prevent swine flu