A portrait of a three-time Mayor of St Albans has been authenticated as a genuine work by the artist Gainsborough by a TV programme.

BBC1’s Fake or Fortune on Sunday evening looked into the provenance of the painting of Joseph Gape which is on loan to the Museum of St Albans in Hatfield Road and was being kept in store.

Now the previously unattributed picture, which was verified by a leading Gainsborough expert, is on display in the foyer of the museum where it will remain until the summer.

Presenter Fiona Bruce and art experts Philip Mould and Bendor Grosvenor found six paintings on the new BBC Your Paintings website that they thought could be attributable to Thomas Gainsborough, one of the greatest British artists of the 18th Century..

They selected two for closer investigation - one of which was the portrait of Joseph Gape who was Mayor of St Albans in 1746, 1761 and 1797 and served as a councillor for more than 50 years.

The research took Fiona Bruce to the county archives in Hertford where she looked at an old newspaper - quite probably the Herts Advertiser which is nearly 160 years old - referring to the death of Joseph Gape.

St Albans Museum curator Catherine Newley took the painting out of the stores so that the TV presenter could take it back to the experts in London.

On first sight of the original, Philip Mould said it looked like a Gainsborough but “a Gainsborough which has suffered”.

The Gape family was once one of the richest and most famous families in St Albans.

They built St Michael’s Manor Hotel in Fishpool Street in 1585 and lived in it as a private house until it was sold to the Newling Ward family in 1965 when it became a hotel.

They were considerable land owners thanks to a fortune which was based on the tanning trade and at least 16 members of the Gape family held the post of Mayor at various times. The family had loaned the portrait to the St Albans museum.

It was suggested in Fake or Fortune that Joseph Gape’s place in society indicated that the portrait would have been painted by an artist of note - a point which was supported when a later painting was shown of him by Sir Thomas Lawrence.

The experts also revealed a portrait of a Mayor of Bristol painted around the same time - 1762 - which was almost identical to it.

The only real sticking point was that the painting appeared to be an oval, something which Gainsborough never did, but examination revealed that it would have been on a rectangular canvas originally.

Cllr Mike Wakely, the council’s portfolio holder for heritage, said: “It is fantastic news that the Museum of St Albans can now attribute the portrait to Gainsborough.

“The fact that Joseph Gape was painted by Gainsborough suggests that he was a man of significant wealth and influence.”