Image caption One of the images released by the National Archives showing unidentified spots around a helicopter

A spectral Luftwaffe World War II jet over Gower, questions about Anglesey's nuclear plant, and terrified Flintshire motorists.

These are just three of the cases uncovered in files released by the National Archives examining UFO sightings across Wales.

The papers span four decades, and include nearly 7,000 documents.

But one of the biggest Welsh UFO mysteries, the 'Dyfed Triangle', may have been an elaborate practical joke.

It is the latest in a growing number of documents released detailing the UK's obsession with claims of extra-terrestrial sightings that began to surge in post-war Britain.

The papers reveal that between 1996 and 2008, more than 20 detailed sightings were reported to the police and Ministry of Defence in Wales.

I've always been sceptical about these things, until tonight Eye witness to 1996 sighting

'Not a crank'

They include the case of a sighting near Rhossili Bay on the Gower peninsula in September, 2005, describing the UFO as appearing like a WWII Luftwaffe prototype jet.

"Suddenly we became aware of a bright object, travelling at very high speed, moving horizontally from west to east almost directly above our heads," recorded the un-named observer, in an explanation to the Ministry of Defence.

"The object was shaped like a pair of stubby swept-back wings, meeting at around 90 degrees. The wingtips were round, as was the forward joint of port and starboard wings.

"My cousin turned to me in surprise, and I exclaimed: 'What on earth was that thing we just saw?'.

Image caption The Dyfed Triangle aliens? A picture drawn by a Broadhaven pupil in the 1970s

In response, the MoD said it only investigated threats to UK airspace, and had no remit to examine 'aerial phenomena'.

Some nine years earlier, the files recount a sighting by a driver in Flintshire, in August, 1996.

A police record passed to defence officials stated: "The object was very large and bright. It had flames coming out of the rear and there was no noise coming from it at all. It was 20ft from the ground and moving very fast."

The report said the sighting was made towards Mold, and the records notes that the driver was "extremely shaken-up by the incident".

Significantly, two other sightings were made on the same day - one on Anglesey, and another not far ways from the first at Chirk.

"I've always been sceptical about these things, until tonight. I've never seen anything anything like it in my life before," said one witness.

Another incident found its way to the the House of Commons, after concerned residents near Wylfa nuclear power station on Anglesey contacted the then MP, now assembly member, Ieuan Wyn Jones.

He wrote to ministers about the alleged sightings, seeking reassurance.

... there is general speculation in the neighbourhood that a practical joker may be at work MoD official on the Dyfed Triangle

However, officials were unable to address the mystery or confirm whether the so-called UFO was in fact a search-and-rescue operation from RAF Valley.

"It would have been highly unlikely that any of their helicopters would have been airborne," said officials.

Wales' 'Roswell incident'

Finally, the full records regarding the so-called 'Dyfed Triangle' have been released, after some of the papers were made public in 2010.

It has widely been viewed as Wales' own 'Roswell incident' - sightings of both UFOs and aliens in an area stretching across parts of Pembrokeshire and Ceredigion in the 1970s.

One incident recalls a sighting by Rosa Granville who ran a hotel in Little Haven. She was woken late at night and saw what she described as a flying saucer ship, and then a silver alien shape.

Similar stories were told by schoolchildren at Broadhaven.

The MP at the time, Nicholas Edwards wrote: "I am being inundated at the present time with representations about UFOs said to have been seen in Pembrokeshire."

But the files reveal that officials who investigated the incident suspected pranksters.

"The Community Relations Officer added that there is general speculation in the neighbourhood that a practical joker may be at work," wrote staff at S4 - the government department that investigated sightings at the time.

"RAF Brawdy have had other enquiries about men in silver suits and it is perhaps not irrelevant that a local factory manufactures clothing of this type for the oil installation at Milford Haven."