The Folger portrait of Shakespeare in its original state

When art conservators joined hands to restore two rare portraits of Shakespeare they thought they were removing paint daubed on the canvases more than 100 years after the Bard's death to reveal "authentic" portraits beneath.

Now it has emerged they were, in fact, wiping away priceless insights into the changing appearance of Britain's greatest playwright.

The images which had been superimposed on both paintings had actually been painted in Shakespeare's own lifetime, the Art Newspaper will reveal next week, and showed how he looked as he aged. The so-called "restoration" could now go down in art history as one of the biggest blunders on record.