At the time of the theft, a spokesman for the museum said the painting was too "well-known" to "sell on the open market".

BBC: Stolen $1m Henri Matisse recovered

The re-working was said to have followed a dismissive comment by a visitor to Wallington who called the work "a painting of a hat and ruffles" - but the identity of the real artist is still open to speculation.

BBC: Thomas Gainsborough portrait 're-worked by rival'