An early portrait by artist John Constable has been discovered and is due to be sold by Sotheby's, the auction house has said.

The painting, The Daughters of Mr W Mason of Colchester, is due to go under the hammer on 13 June, and is expected to fetch between �50,000 and �80,000.

Its existence was previously unknown to art historians.

The Mason family lived in Jupe's Hill, in Dedham, near Colchester, Essex - the neighbouring village to East Bergholt, the artist's birthplace.

'Landscape'

Mr Mason was the artist's lawyer, and the portrait is believed to have been painted in lieu of payment of a debt.

It then passed through successive generations of the family.

It was found by a fine art valuer during a routine valuation at an unidentified house in East Anglia.

The find was authenticated by Graham Reynolds, one of the country's leading Constable scholars, Sotheby's said.

In-house art expert Henry Wemyss said the only known reference to the work was in a 1937 edition of an 1840s memoir by a friend and biographer of the artist.

He said Constable had enjoyed painting "young ladies with an open window and a landscape beyond".

"It was a device he liked," he added.

Before Constable became established as a master of English landscape painting, he painted numerous portraits, of individuals and of groups.