Fiona and Philip attempt to help Martin Lang try and prove the painting he bought in 1992 is by modern master Marc Chagall.

Fiona and Philip attempt to help a man who believes he owns a painting by French post-impressionist Edouard Vuillard.

Fiona and Philip attempt to prove that two paintings are missing works by one of the country's best-loved artists, John Constable.

This week the focus is on Britain's public art collections, in which 17,000 paintings are listed as `artist unknown'. Philip identify several works they believe are by Thomas Gainsborough.