THIS unrecorded portrait by John Constable, estimated to make up to £80,000, was discovered by East Anglian auctioneer and fine art broker John Vost during a routine valuation at a house on the Suffolk/Norfolk border.

The Daughters of Mr W. Mason of Colchester, 2ft x 20in (61 x 51cm) has been authenticated by two Constable scholars and will appear at Sotheby’s major British and Irish pictures sale in London on June 13.

An inscription on the stretcher read Constable, 50, Rathbone Place, an address just off the Tottenham Court Road, and further research identified a brief reference to the work in G.R. Leslie’s famous memoir of the artist.

Henry Wemyss, Sotheby’s picture specialist, said the portrait of the four girls had been dated to 1806 and was similar to The Brydges Family, another group portrait from the early 1800s now in Tate Britain.

“I was called out to do a valuation and spotted this picture among a number of minor paintings hanging on the sitting room wall of the house,” said Mr Vost.

“Over the years you develop a sixth sense about these things and as soon as I saw it the adrenaline started to flow. It just stood out as a Constable.”