Art experts have discovered an unseen oil sketch of Hampstead by Romantic painter John Constable which had been concealed behind another of his works for at least 125 years.

Ham & High: Branch Hill Pond: Hampstead by John Constable. Picture: Victoria and Albert Museum, London.Branch Hill Pond: Hampstead by John Constable. Picture: Victoria and Albert Museum, London. (Image: (c)Victoria and Albert Museum, London)

Conservators at the Victoria and Albert Museum (V&A), in South Kensington, uncovered the painting on the reverse of Constable’s seminal landscape work Branch Hill Pond, Hampstead.

The piece, which depicts a clearing fringed by trees along with a mix of dark clouds and blue sky, was unearthed beneath a lining canvas that had been attached to the Branch Hill Pond painting as support but had become loose over the years.

While preparing Branch Hill Pond for a major Constable exhibition at the V&A next year, the conservators removed the loose lining canvas and discovered the oil sketch.

Mark Evans, the V&A’s senior curator of paintings, said: “The recent discovery is a rare and enormously exciting event. Constable was thrifty with his artist’s materials and sometimes painted sketches on both sides of scraps of reused canvas.

“This scene painted on the reverse of another sketch had been concealed for well over a century beneath a lining canvas.”

The newly-discovered scene is believed to have been painted in the late summer of 1821 or 1822 in Hampstead, when Constable painted a number of sketches featuring similar cloud studies and motifs while living and working from a home in Lower Terrace.

Describing the new discovery, Mr Evans added: “It depicts a narrow clearing fringed by trees set against an unsettled sky, and in the foreground what appears to be a smoking brick kiln, which were a common sight on Hampstead Heath during the Regency building boom.”

In 1888, Constable’s last surviving child, Isabel, gave the remains of her father’s studio contents - three easel paintings, 92 oil sketches, 297 drawings and watercolours and three sketchbooks - to the V&A.

Six of the oil sketches bequeathed to the V&A were previously known to be double-sided. In the past, X-radiography had revealed evidence of another composition on Branch Hill Pond but it was assumed that these were traces of an over-painted scene on the front.

The previously unseen Constable piece went on display at the V&A today. It will also feature in an autumn 2014 exhibition Constable: The Making of a Master.