Are we all alone in the universe? Nick Pope, former head of the government's UFO investigations, isn't so sure. He talks to Raf Sanchez about the great 'unexplained'.

To conspiracy theorists, Nick Pope is the right man with the wrong answer. The former head of Britain's UFO Project has had years of unparalleled access and resources to investigate the significance of unexplained visitors to Britain's airspace. Since leaving the MoD in 2006 he has taken up a high profile career as a writer, lecturer and consultant. He seemed to be a man preparing to impart revelation. If anyone should be able to confirm that the government knows of the existence of extraterrestrial life, it should, in theory, be Pope.

Except that he won't. To the rabid frustration of many Ufologists (the recent term coined to describe those who study UFO sightings) Pope continues to deny that the government he served for over 20 years has information confirming the existence of aliens and just isn't sharing it. Clips of interviews on the internet show the clean cut former civil servant interrogated by enthusiasts already sure of the answer they want and left bitter and accusatory when they don't get it.

Despite his consistent response to questions about a cover-up I decide to try my luck, just in case he is having a particularly candid afternoon. His answer is swift and well-rehearsed. "To the best of my knowledge, there's no cover-up and no conspiracy. While the MoD has consistently tried to downplay the subject, they've never lied about it and have no evidence that would prove the existence of extraterrestrials. Where information is being withheld, it generally relates to details that if released would be detrimental to defence or national security." He says that there are vast case files of incidents and sightings that his unit was never able to explain away as weather balloons or airplanes but what there isn't is, as Pope puts it, "a smoking gun", or more bluntly: "something locked away in a hangar somewhere."

I find his answer convincing enough, except for the fact that as a signatory to the Official Secrets Act, it's the only one he can give without opening himself up to the possibility of prosecution by his former employer. How can we believe his denial when it's the only thing he can legally say?

I put this to Pope, who nods resignedly at his dilemma. "I do appreciate I'm in a very difficult situation. We're back to that old cliche that you can't prove a negative. I can understand why I get accused of disinformation and all sorts of things but I don't think that there's anything I could say, even if I could come up with the most eloquent, well reasoned, logical, substantiated argument. If a die hard conspiracy theorist really wants to believe something, my denial is not going convince them otherwise."

For the record, I believe Pope. He seems too interested in the details of UFO sightings, too energised by the fragmented information they afford - details which would surely be swept away by the blanket knowledge that aliens definitely exist. More than that he seems genuinely philosophical about the impact that such knowledge would have on humanity. "I think that it would be, aside from proof of the existence of God and an Afterlife, the next biggest thing that you could ever hope to discover and the world would obviously be a totally different place the day after we knew for sure we weren't alone in the universe."

The interesting thing about Pope is that his career follows an inverse trajectory to most of those in the UFO business. Rather than being someone who was convinced from the outset of the significance of UFOs and went about gathering information, Pope had the information before the belief. Before taking over the UFO Project (his brief had no official title but 'UFO Project' is his preferred term because "it does what it says on the tin") he served in a number of more traditional roles within the MoD. During the first Gulf War he assessed the impact of Allied bombing raids on Iraqi positions and was responsible for briefing senior government and military figures.

Pope claims he arrived at the job with a "broadly skeptical" view as to the wisdom of putting resources into investigating UFOs. His remit could be summed up in a single line: "to evaluate UFO sightings to see whether or not there is evidence of anything of defence significance." It is these last two words that shaped the focus and operating procedures of the unit. "Defence significance is the key phrase that over the years has been interpreted in many ways. Skeptics can take it to say 'well, we're only interested in foreign military aircraft.' Someone a little more open minded can say 'Well no, if UFOs really are extraterrestrial then that would be of defense significance in and of itself.'" It seems difficult to argue that alien craft entering British airspace would not be of interest to defence intelligence, but apparently it was a line taken by some of the more traditional members of the military establishment.

Challenging this view and instilling a sense of the importance of the "belief that UFO sightings should be properly investigated in a scientific way" has been one of Pope's passions both within the MoD and since leaving the government. In November 2006, shortly after leaving the Ministry, Pope made headlines (some wryly amused, others alarmist) with his claim that the UK's air defence was "wide open" to any potential extraterrestrial visitors, friendly or otherwise. The Daily Mirror ran with: "Earth: We're Wide Open To Attack".

So what did Pope see during his time at the UFO Project that not only converted him from a skeptic but has turned him into something of a campaigner for a scientific approach to Ufology? The answer lies in a proportion of 5%. Pope found that of the 200-300 reports of UFO sightings that came across his desk every year, 80% could be explained away as "misidentifications of something ordinary, such as aircraft lights, satellites, airships, weather balloons or planets." In a further 15% the information was too sparse to make any real judgments. Yet, in the remaining 5% there was enough information, usually in the form of radar signatures and visual sightings by trained observers like RAF pilots, yet still no one was able to identify the object. To Pope these incidents were "very interesting and by definition 'unexplained'.

The 'Cosford Incident' helped to solidify Pope's belief that something had to be done to deal with the vulnerability of Britain's air defence to penetration by UFOs. On the night of March 30 and the morning of March 31 1993 over a hundred witnesses, many of them pilots and police officers, reported seeing fast moving lights in the sky. Some gave more detailed descriptions of a large triangular shaped craft, "like two Concordes flying side by side and joined together." Another sighting was then reported by an officer, at an RAF base in Shawsbury.

"He saw the UFO fire a narrow beam of light (like a laser) at the ground and saw the light sweeping backwards and forwards across the field beyond the perimeter fence, as if it were looking for something. He heard an unpleasant low frequency humming sound coming from the craft and said he could feel as well as hear this - rather like standing in front of a bass speaker. He estimated the size of the craft to be midway between a C-130 Hercules transport aircraft and a Boeing 747." No aircraft were scrambled because the object, seen in over a hundred places, could not be detected by radar.

Pope, who has been sitting forward intensely as he talks, suddenly smiles and leans back. "My head of division, who was a huge skeptic of UFOs, briefed the assistant chief of the air staff [on the incident]. There was this wonderful phrase: 'In summary, there would seem to be some evidence that on this occasion an unidentified object (or objects) was operating over the UK.' That's probably about as close as the MOD will ever get to saying there are UFOs."

Although he is quick to point out that his background is defence intelligence and not science, Pope can be coaxed into talking interestingly on scientific developments in man's search for other life in the universe. He is quick to draw a distinction between Ufology, the study of UFOs that enter Earth's atmosphere, and the Search for Extraterrestrial Intelligence (SETI). "Ufology," he says "is a broad church. There are some complete nutcases and charlatans involved in it and there are also some extremely professional men and women doing some sterling work." Ufology as it currently stands has no established scientific method and can come in any number of forms, from sitting on a hillside with binoculars to the kind of intelligence analysis that Pope was employed in.

SETI is a much broader search than simply looking out for alien craft coming to Earth. It relies mainly on the use of enormous radio telescopes to monitor deep space for signs of intelligent transmissions. And the already advanced technology is moving fast. According to Pope, "the sensitivity and power of the radio telescopes and the associated computing power to analyze and process the data is going through the roof." In 2014 the next generation of radio telescopes will come online, massively expanding humanity's view of the Universe. The technology is so powerful "there are scientists who believe that if there are detectable civilizations within a 100 light years of here, which certainly encompasses several thousand stars, we should be able to detect them through their signals." The thought that in less than a decade human technology could push the shadows of space back so far is both awe-inspiring and terrifying.

Pope puts his faith in SETI to make the first contact with other intelligent life forms. "I believe that if contact is made it will come through radio astronomy, through detecting a signal as opposed to a spaceship landing in the desert. Proof of contact is never going to be a photo or a video or something. It has to be something acknowledged by the mainstream scientific community. Which is why I think it's far more likely that proof will come through radio astronomy. SETI will beat Ufology when it comes to proof positive, simply because society will not accept what Ufologists regard as proof."

Interestingly, SETI today is "effectively private". The highly technological operations are carried out by private research organisations and members of the scientific community rather than by governments or militaries. NASA briefly engaged in SETI in the first half of the Clinton administration, before a cost-cutting Republican Congress pulled the plug on the project in 1996. Since then the search has been carried out almost entirely outside of government quarters. The UK's largest radio telescope, Jodrell Bank, is run and maintained by the University of Manchester. This raises the slightly bizarre situation in which the first people to make contact, and possibly speaking on behalf of Earth, may not be one of the world's governments but instead the employees of a private research company.

This lack of a plan, or even a framework, for dealing with the discovery of aliens is another of Pope's concerns. "What there isn't, as far as I've seen, is any contingency plan, any SOP [standard operating procedure] for a landing, a crash, a contact. I think in a sense that is a mistake. The military and the government tend to have a plan for just about everything. There are some serious issues that would need thought, bio hazards to name just one. If there is open contact one of the questions people will ask is 'is there a bio hazard from us to them, them to us, or indeed both ways, who is going to test for that, how is it going be tested, what kit is going to be used, where is that kit, how do you get it to the location, what are the command control arrangements, what's the media handling strategy?' All these questions, not any plan. Frankly, we'll just muddle through."

Although, as Pope admits, in the event of a landing by a race that can travel at lightspeeds, it is unlikely that humanity is going to be in the driving seat and the best-laid plans of men often go awry. "Any civilization that visits us is almost certainly going to be more technologically advanced than us, so chances are they are going to be the ones that dictate whether or not it's kept a secret and on what terms contact is made and on what terms the news is propagated. If we are visited it might well be that the visitors set the agenda and call the shots."

Pope may not have seen confirmation that there is other intelligent life in the universe. But what he has seen, and it is likely to be far more than most of us ever will, seems to have convinced him of the need to be prepared that one day there might be. As I think of the epic bureaucratic, administrative and logistic battles a plan for a human response to contact would bring I find myself wondering if somewhere out there someone has a much simpler plan for us.