Mr Strachan said that two Reynolds experts had looked at the painting, with one telling him “he found no reason to think it was not by Reynolds”.

He said the painting had been in a state of neglect when he found it, despite some 19th-century restoration work. 

“The panel had cracked in the past and it had had quite a lot of broad overpaint to conceal the cracks,” Mr Strachan said. However, once that paint was removed, its provenance became clear.

If it is indeed a Reynolds, it would be among his rare “fancy” paintings – a term used by the artist himself to describe his non-portrait works.

Reynolds, who was born in Plymouth in 1723 and died in London in 1792, was known mostly for portraiture. However, when working for his own pleasure, he often experimented with new forms and different styles.

Only around 20 or so of Reynolds’s fancy paintings are known to exist.

The painting being sold on Thursday depicts two young girls playing in the woods and is said to be more sentimental than much of his work. However, his fancy paintings often depicted young women and girls enjoying themselves.

Mr Strachan would not reveal the exact asking price for the painting but said it was under £50,000.