A copy of Magna Carta, one of the most important documents in British history, was secretly hidden in a cave in Wales during the Second World War.

Paintings by Michelangelo, Raphael and Leonardo da Vinci were also among a treasure trove stored in a specially-built underground chamber near the National Library of Wales in Aberystwyth.

Researchers delving into the institution's archives revealed that the cave was also temporary home to the oldest copy of the New Testament, the works of Chaucer and letters written by the kings and queens of England.

The mass evacuation of precious artefacts from around the UK to Wales in the event of a war in Europe had been planned from 1933 onwards.

Within hours of the declaration of war in 1939 collections from many cultural institutions were crated up and sent by rail to Aberystwyth.

The collections of the British Museum took up 25 containers, with the material weighing more than 90 tons.

The secret operation came to light when staff at the National Library of Wales looked into their archives to research an exhibition of Da Vinci drawings now on display there - and found that they were amongst items to have arrived on the eve of war.

Medi Jones-Jackson, communications officer at the National Library of Wales, said: "It's amazing to think some of the most historically important documents and artworks of our times were kept safe here in Aberystwyth.

"The cave was built with specialised ventilation and heating systems to protect the valuable items placed inside."

It was built in to the side of a hill to avoid the risk of artefacts being hit by stray bombs dropped from planes chased away from industrial centres.

Cultural historian Professor Peter Stead said: "London was bombed for 96 consecutive nights during the Blitz so the great artworks needed to be removed for safekeeping. Paintings don't like too much light so, of course, the caves were ideal places to store them."