Every week, Philip Mould breaks the hearts of fellow art dealers as he reveals the disguised masterpieces they let slip through their fingers on the BBC’s Fake or Fortune?

But on Sunday night it was the presenter himself who was forced to face up to what might be described as a £2 million mistake when the art detective show discovered an authentic Constable he had previously sold for just £35,000.

For 17 years, a depiction of Willy Lott’s Cottage on the River Stour has hung – with dubious provenance – on the wall of Gloucestershire businessman Henry Reid.

Now, using groundbreaking technology and an investigation that ranged from Los Angeles, Perthshire to London’s Savoy Hotel, the work has been confirmed as a prototype of the iconic Hay Wain, which depicts the same scene.

Constable scholars have described the discovery as “very important indeed”.

Yet when Mould, then a fledgling dealer, owned the painting on two separate occasions in the 1990s, he could find no one prepared to authenticate it.

Experts are acutely cautious of potential Constables, as the artist was the most prolifically forged of the 19th Century. read more