A tiny watercolour painting of Sir Walter Scott is exciting art historians who think it may be a previously unknown work by the artist JMW Turner.

The postcard-sized picture of the Scottish author depicts him and his family at their Abbotsford home, near Tweedbank in the Borders.

It was bought by the Abbotsford Trust after it was discovered in a London auction house by trust members who became intrigued by the possibility it was by the famous English Romantic artist.

If the painting is authenticated as a Turner, it will be worth millions.

One of the last of the artist's masterpieces which remained in private hands set a world auction record when it sold in 2014 for £30.3 million.

Turner, who first explored the Borders, aged 22 in 1797, met the Ivanhoe-author several times.

It is thought the small painting, which is 5.5 inches by 3.5 inches, was created during a visit he made to Abbotsford in the summer of 1831.

It is currently on show at the Abbostford museum — situated in the writer's former home — in an exhibition entitled Turner and Scott: The Painter and the Poet.

The trust is now supporting ongoing research into the painting, with researchers and scientists analysing the work.

As written in the Scotsman, the painting has been subjected to pigment analysis and infrared imaging in an attempt to establish its provenance.

Kirsty Archer-Thompson, collections and interpretation manager for the trust and curator of the exhibition, said: "This painting is, quite frankly, electric.

"Everything about it, from the minutiae in the detail and the use of scraping out highlights, to the evolution of its composition from pencil sketch to painting - a whole world only visible through infrared scanning - suggests to me that it is not the work of a copyist.

"All of this analysis, including work by painting analysis expert Libby Sheldon, demonstrates that it was executed by an astonishingly skilled hand.

"Turner was a master of these highly intricate and delicate watercolour illustrations, two of which are already owned by the Abbotsford Trust.

"Everything about this little painting feels authentic and consistent with the great man. I hope that we can prove the theory with the help and support of enthusiasts and experts in the art world."

Trust chairman James Holloway, a former director of the Scottish National Portrait Gallery in Edinburgh, said: "It is wonderful for Abbotsford to be able to show such a fascinating painting.

"It will intrigue and delight our visitors. To think that we are publicly displaying the watercolour for the very first time since it was painted by Turner is also tremendously exciting."

If found to be genuine, the painting may be an early version of another painting of Abbotsford used as the inspiration for an engraving published in Memoirs of the Life of Sir Walter Scott, a commemorative biography published after the writer's death.