TV portrait of Turner lets a few cats out of the bag

The paintings of J M W Turner are prized and worth millions, but it wasn't always thus. When the cats that populated the great man's damp and leaking studio needed an exit, the artist simply cut a catflap in one of his works- in-progress, a new documentary reveals.

In the programme, Joyce Townsend, Tate Britain's senior conservation scientist, describes the reckless use of one such painting, Fishing Upon The Blythe-Sand, Tide Setting In. "He used one canvas as a catflap. It was blocking a window, possibly even a broken window," she says in Turner: The Man Who Painted Britain, to be broadcast by BBC1 on Sunday.

Turner's cats appear to have the run of his studio, even walking across the back of drawings he had prepared for teaching at the Royal Academy. Ms Townsend tells the programme: "I haven't found any cat hair, but I found some paw prints."

The documentary, presented by the art historian Tim Marlow, may surprise those who know the gorgeous sweep of Turner's paintings but nothing about the man. It details his relationship with a widow by whom he had illegitimate children and an affair with the owner of a boarding house in Margate. He never acknowledged either liaison publicly.

And it recounts how after his death at the age of 76 in 1851, John Ruskin burnt dozens of drawings Turner had made of prostitutes. Ruskin feared the great man's reputation would be destroyed if the drawings' existence was made known.

Ruskin should not have worried. Turner's reputation is so high today that even the "catflap" painting is considered important enough for display. The repaired work is currently on loan from Tate Britain to a museum in the United States.