Prolific art forger's paintings up for sale

He had the dubious reputation of being the world's most prolific art forger. Until his death, Eric Hebborn churned out works in the style of the old masters - Rubens, Van Dyck and even Michelangelo.

His paintings were so convincing he fooled experts in some of the top international galleries. But how did he do it?

Clues to the answer are revealed as some of his sketches go on auction tomorrow in Wiltshire. Here's Martin Dowse.