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Robert Warren, the unfortunate art dealer who sold the masterpiece to Mr Tutt, revealed it had been one of a pair and that he had sold the other on eBay but could not remember who bought it.

Another of Vuillard's paintings, called Les Couturieres, sold for more than £5 million in a Christie's auction in 2009 and experts value the newly discovered works at around £250,000 each.

Philip Mould, co-presenter of Fake or Fortune, said: "This is a wonderful example of what can happen in this programme.

"In the course of making the programme we threw everything into the pot in terms of forensics, science, historical (provenance) research, and even established that it been painted in distemper made from boiling hot animal glue.

"An amazing add-on has been to prove that now there is out there, possibly hanging above someone's fireplace, this further missing treasure. And they almost certainly don't know it."

Fiona Bruce, who co-hosts the show, added: "You can't miss this painting, it's very large at four feet high and an unusual oval shape. Whoever bought it off eBay has bagged themselves the bargain of the century.

"We've done all the forensic and investigative work to prove it's genuine, now we just need to find the owner and tell them the good news. Someone, somewhere in the world is sitting on a fortune."