According to the National Gallery, it is a Gainsborough masterpiece celebrating a marriage, starring a fashionable young couple and an unfinished spot on the bride’s lap for a future child to be painted in.

That description, according to an art historian, should be swiftly updated, to take in a new theory: the artist was sending up his subjects with a series of rude symbols while hell-bent on revenge.

James Hamilton, author of a new biography on Gainsborough, said he believed the painting of Mr and Mrs Andrews, owned by the National Gallery, should be immediately reappraised, admitting the true nature of the work was so scandalous they may need to be careful in their wording.

His new book details his reexamination of the famous painting, recasting it not as a celebration of the union of two landed families, but a bawdy mockery of the Mr and Mrs Andrews he had fallen out with.

“Certain signs point towards the painter’s revenge,” he said.

Among the hidden signs Hamilton claims to have identified are two donkeys trapped in a pen, added in the far background to the left of the painting, a “phallic” bag tied to Mr Andrews hip complete with “floppy leather glove” and a doodle of a penis in Mrs Andrews’ lap.