The news has only been out less than a week, but already one museum has inquired about the availability of the Shaw Burns, the portrait of the Bard which was discovered at a provincial sale room in England, and revealed to the world by The Herald this week.

The discovery of the portrait of Robert Burns, a version by Alexander Naysmith (1758-1840) of his own original work, which currently hangs in the Scottish National Portrait Gallery in Edinburgh, is one of the those stories that does not come along too often.

Much of the credit for the research of the painting – currently with its owner, south of the Border – goes to Jerry Brannigan, a Glasgow-based writer (a heating engineer by trade) who spent many hours piecing together a credible and persuasive case that the work was once owned by Sir James Shaw. Sir James was a fascinating character himself, an Ayrshire lad made good, who rose from humble rural stock to become the Lord Mayor of London. A real life Dick Whittington, really.

Sir James, as Mr Brannigan told me, was also very close to the Burns family, his widow Jean Armour, and spent money on the poet's children's schooling as well as finding his sons employment.

How the painting got into Sir James's hands is unknown, it may have been a gift from Ms Armour, but he could also have bought it from Naysmith – Sir James had a considerable art collection. The back of the painting's frame, which is very late 18th century, has his name inscribed, as well as a tag that reads "Edinburgh".

The owner, who I spoke to at length last week but who is keeping his identity secret at the moment, has educated eyes. He saw the painting at the sale and knew it was worth more, and was far more interesting, that the unfortunate auctioneers selling it thought it was. Initially he thought it may be a long-lost portrait by Sir Henry Raeburn. So he took it to the pre-eminent Raeburn expert, Dr David Mackie of Cambridge University.

Dr Mackie is currently writing what is likely to be the definitive catalogue of Raeburn's works, to be published next year.

He quickly ascertained that the painting was not Raeburn, but Naysmith seemed a great possibility.

Dr Mackie made a trip to Edinburgh, to see the original, and, judging the new Burns picture by its style, its age, and other aesthetic features, was happy to confirm it was by the noted Scottish painter.

Dr Mackie was happy to stake his name and reputation on the painting, which, for the owner, was a satisfying conclusion to his speculations. And is likely to earn him a little windfall when he sells it on, as he wishes to.

He wants to sell it for £2 million – which may be a little optimistic. But who would buy it? Kelvingrove Art Gallery has a Naysmith Burns, as does Edinburgh and London. After so many years hidden to history, it would be a shame if it was lost to a private collection again.