One evening in January 1974 at Llanderfel, near Bala in Mid-Wales, there were lights in the western sky and a bright flash on the Berwyn Mountains, followed by earth tremors and a loud bang. People came out of their homes and the pubs to see what had happened. Within a couple of hours the armed forces had arrived, and ‘men in black’ a day or two later. People who tried to follow the army trucks up the mountain lanes were ordered back. But the military has always denied that a UFO crashed. There are reports of large pieces of metal being recovered from the hills and rumours of alien bodies being recovered still persist.

The philatelic interest lies in the use of unusual MOD £1 revenue stamps, with a pair of the even rarer specimen stamps, on highly confidential military communications, and a souvenir label sold locally to cash in on the story