Welsh 'Roswell' one of UFO file highlights

A famous UFO incident dubbed the "Welsh Roswell" is one of the highlights from the latest batch of UFO files released by the Ministry of Defence (MoD).

Locals heard a huge bang and saw a brilliant light in the sky over the Berwyn Mountains in north Wales on the evening of January 23, 1974.

Some researchers have claimed the explosion was caused by an alien spaceship crash that was covered up by the authorities.

But an investigation carried out by the MoD concluded that the scare was the result of a noisy earth tremor that coincided with a meteor burning up in the atmosphere.

The previously top-secret files also show how RAF jets were scrambled to investigate UFOs picked up on radar 200 times a year during the Cold War.

This fell to zero after the collapse of the Soviet Union in 1991 as Moscow stopped sending anti-submarine aircraft and spy planes into British airspace.

Another highlight in the files reveals how a gambler appealed to the government for help after a bookmaker refused to pay out on his 100-1 bet that aliens would land on Earth.

The punter had a bet with Ladbrokes on extraterrestrials being found dead or alive by the end of the 20th century.

Ladbrokes refused to pay out, writing to him in April 1999: "We advise that at present your bet is not a winner as the United Nations, who we use as our source of authenticity, has not yet confirmed the existence of aliens."

Asked to intervene, the MoD agreed there was no evidence of visits by lifeforms from other planets and backed Ladbrokes.

The punter complained to the Ministry which brought this official response: "To date the MoD is not aware of any evidence that might substantiate the existence of alien lifeforms and therefore supports the view that your bet should not be upheld."