BBC_ The oil painting sketch, The Harvest Field, dates back to 1797 and has a guide price of £40,000 to £60,000.

It will go under the hammer at Sotheby's Auction House in London on Friday.

Sotheby's cataloguer Giorgio Bowler said it shows the Suffolk-born artist "developing his own unique style".

He said the work remained unknown to art scholars until 1992 when it was last sold for £34,100. It is part of a private collection.

The sketch is one of two depicting the same scene, with the other showing the figure in the lower right in a red coat, and the number of birds in the sky differing.

'Subtle colouring'

Mr Bowler said: "Prior to its appearance on the market in 1992, the work was in a private collection in the US and was completely unknown to scholars.

"As it often happens with Old Masters, artworks can remain treasured in private collections for centuries and only rediscovered when presented for sale at auction."

He said the work is "particularly appealing" to collectors of Old Masters.

"Constable sketches are highly sought after and provide a fascinating insight into the artist's working method.

"Executed in 1797, this sketch shows Constable developing his own unique style, taking inspiration from great masters of Dutch landscape painting as well as his immediate forebears such as Thomas Gainsborough.

"This is particularly felt in the subtle use of colouring and the fascination for capturing minute details and textures," he added.

Born in 1776 in East Bergholt, Constable is best known for his depiction of the English countryside, particularly his native Suffolk.