The picture, a View of Ipswich, was found and identified by art sleuth Philip Mould who specialises in tracking down lost paintings.

A spokesman for the London art dealer said he is offering the painting to the artist’s birthplace museum Gainsborough’s House, Sudbury for £750,000.

Diane Perkins, director of Gainsborough’s House, said it would be wonderful if the painting could come to Sudbury and they were investigating the possibility of buying it.

“It’s a really important painting because it shows a recognisable Suffolk view and Gainsborough rarely painted identifiable places.

“We would have to go to the main funding bodies like The Art Fund and the Heritage Lottery Fund and ask for grants.

“We would probably have about three months to raise the money.”

Dr Bendor Grosvenor, director of Philip Mould’s London gallery, said the picture first surfaced in December last year at an auction in London where it was described as a work by an unknown artist.

The “art detective”, who has recently published a book about his search for lost paintings, paid £67,250 for it.

Research proved it was a previously unknown work by Gainsborough, painted in the late 1740s when the artists was in his late teens or early twenties.

It shows a view of Ipswich including Christchurch Mansion, which still exists today.

Philip Mould’s research established that the picture had once sold at auction in London in 1824 described as A View of Ipswich from Christchurch Park by Gainsborough, and had belonged to the renowned collector George Nassau.

Nassau’s father had been painted by Gainsborough in Ipswich in the 1750s, and it is believed that the Nassau family may have acquired the picture then.

Mr Mould said: “I very much hope that this painting can end up in the museum of his home town. It has been the most thrilling experience piecing together its forgotten history, and a further reminder of how great a British artist Gainsborough was at a young age.”

Mrs Perkins said the real clincher that the picture was genuine was its brilliant provenance. “Also, Christchurch Mansion was owned by the Fonnereau family, who Gainsborough knew,” she said.

Another long-lost Gainsborough accepted by most experts to be an early version of his famous Cornard Wood - and also tracked down by Mr Mould - was unveiled to the public at Gainsborough’s House in May and was on show there for a month.

barbara.eeles@sudburytoday.co.uk