A major portrait of Archibald Campbell, 3rd Duke of Argyll, the founder of the Royal Bank of Scotland, and one of the 31 Scottish Commissioners who negotiated the 1707 Act of Union with England, is to be sold at Bonhams Scottish Art sale in Edinburgh on 19 April.

The painting, which is estimated at £20,000-30,000, is by Allan Ramsay, one of the greatest and most influential portrait painters of the 18th century. Ramsay also painted the portrait of the Duke which has appeared on all Royal Bank of Scotland bank notes since 1987.

Chris Brickley said:- “The emergence onto the market of this major work by Ramsay could hardly be more timely with RBS constantly in the news and vigorous debate taking place over the future of the Union between Scotland and England in which Campbell played a persuasive role.”

Ramsay enjoyed the Duke’s patronage and friendship for more than twenty years and painted him a number of times. This portrait is more intimate than the grander ceremonial works and it is known that Ramsay used it as the primary image of the Duke from which he derived later portraits.

The painting is dated 1748. Ramsay visited the Duke in his London residence in August that year, but then travelled with him to Scotland and in September was his guest at Inveraray Castle. No-one knows for sure whether the picture was painted in London or in Argyll but Inveraray Castle is the more likely as the picture seems to be entirely by Ramsay’s hand. In London he still used assistants at this date, but no assistant would have travelled north with him.