Hidden sketches by the likes of Michaelangelo, Leonardo da Vinci and Raphael have been discovered by experts at the British Museum.

They found the "underdrawings", which had been erased by the artists, with new techniques developed for drug detection and forensics.

One of the images reveals that Michaelangelo based his Bruges Madonna sculpture on a male model. At the time women rarely sat as models for artists.

The sketch was found beneath a later drawing for the sculpture, but the earlier work was invisible to the naked eye.