The UK National Archives has seen record traffic following the release of previously secret Ministry of Defence files on UFOs.

The UFO site details investigations into sightings, alien abductions and crop circles from 1978 to 2002. It attracted 264,285 visits on the first day, five times the normal level.

Information is contained in eight PDFs totalling just under 240MB which were downloaded over 1.3 million times in the first four days.

The site includes an introductory videocast by ex-MoD investigator Nick Pope and a PDF or podcast guide to the new files by UFO historian Dr David Clarke of the Department of Journalism and Communication at Sheffield Hallam University.

"If you want to find out more about lights in the sky over Waterloo Bridge, near misses by pilots, crop circles and what the UK government thought of it all this is the place to start," says the introduction.

The files have already created a huge surge in demand for UFO material. Web searches for 'UFO' increased by 267 per cent overnight, according to Hitwise logs.