When Ann Widdecombe declared that there was "something of the night" about Michael Howard she could have had little idea that there had already been an official investigation into whether he had had some unusual ­nocturnal visitors – aliens.

But the opening of the latest batch of Britain's own "X-files" today reveals that the RAF in March 1997 did mount an inquiry into reports from six members of the public, including two firefighters, of a large, triangular "humming" object in the sky above his Folkestone home during his last months as home secretary.

The Ministry of Defence file reports that witnesses said the UFO hovered for several minutes above a field before shooting off in a flash of light. Sophie Wadleigh, 25, from Hythe, told the Folkestone Herald: "It was so peculiar, it all felt really odd and I heard this humming noise. As I looked across the field I saw a large triangular shaped flying craft hovering about 300 feet off the ground."

The MoD file includes a report from Chris Rolfe, of the East Kent UFO monitoring group, which says he believes it could have been looking for the former home secretary, as it was not interested in Wadleigh: "This … has left me wondering if its purpose had something to do with Mr Howard."

Other witnesses described it as being a lot bigger than a plane, with lights around the outside and a disc on the back. The official inquiry into the sighting on 8 March 1997 concluded: "MoD air defence staff have confirmed that there is no evidence to suggest any unauthorised incursion of the UK air defence region on that date." It added that "additional inquiries had confirmed that no unusual or unauthorised air activity, civil or military, was reported or observed in that area on that date".

The incident is one of thousands of reports of what are officially known as "unexplained aerial sightings" in the latest batch of MoD files released today at the National Archives in Kew. The 24 files contain more than 6,000 pages of documentation covering 1994 to 2000.

The government remains officially "open minded" on whether there are aliens among us. The MoD says: "We are often misquoted as saying we do not believe 'UFO/flying saucers' to be a threat; this is a distortion of the MoD's stated position which is that to date we have seen nothing which could be classed as proof that extraterrestial life exists."