A SKETCH by John Constable once dismissed as a copy is set to go under the hammer has sold for £70,000.

The newly-discovered painting shows a view of Dedham Vale and includes a windmill owned by his father.

The work, painted in 1809-10, had hung in a London townhouse for many years.

A London auction house had previously dismissed it as a copy without investigation, but after work by auctioneers Sworders its true identity was discovered.

Pictures specialist Sarah Flynn deemed it worthy of further research and took it to Anne Lyles, the world-renowned authority on the art of John Constable.

She later declared it “an exciting new discovery”.

It went under the hammer at an auction last week with a guide price of £100,000 to £150,000.

It was eventually sold for £70,000.

Sarah said: “It is the dream of every auctioneer to discover a picture by one of the greats of Western art.

“Dedham Vale is intimately associated with Constable’s life, but the inclusion of one of his father’s mills in this picture makes it a particularly personal image.”

The most famous work by Constable of the panorama is the picture titled Dedham Vale, Morning, which he exhibited at the Royal Academy in 1811.

Constable made a number of preparatory oil sketches for this composition, which show the distant towers of various churches in the distance.

The newly-discovered painting is known as Dedham Vale with Brantham mill and haystacks and it shows the distinctive tall tower of Dedham Church in the far right-hand distance.

The viewpoint is thought to be the furthest east Constable ever painted Dedham Vale, and includes windmill at the village of Brantham in the picture.

Constable’s father Golding Constable is thought to have owned it.

Paintings by Constable have previously fetched millions of pounds at London-based auction house Christie’s.

In 2012, an oil painting called The Lock brought in £22,441,250, while View On The Stour which is based on an area near Dedham sold for £14,082,500 four years later.