George Stubbs and Thomas Gainsborough auction records

The painting shows the racehorse Gimcrack in the foreground and background

A painting by the horse-racing artist George Stubbs has fetched £22.4m at auction.

The oil painting, called Gimcrack On Newmarket Heath (1765), has been sold at Christie's in London by the private Woolavington Collection.

The price is a new record for the artist who became famous for his studies of horse anatomy.

A portrait by Thomas Gainsborough sold for £6.5m at the same session - a record for the Sudbury-born artist.

Matthew Paton, from Christie's, said Gimcrack was one of Stubbs's masterpieces and "possibly the greatest horse racing picture that exists".

"It's actually the third most valuable Old Master ever sold, so Stubbs joins a very small group who've sold for over £20m and that includes Rubens, Rembrandt, Pontormo and Turner.

Detail from Mrs William Villebois by Thomas Gainsborough

Record breaker

"The buyer wishes to remain anonymous, so we don't know if it's staying in the country.

"Quite often when you have an exceptional price for an artist, then if you've got another work in your collection, it prompts you to have it re-appraised and re-valued."

The painting, whose full title is Gimcrack On Newmarket Heath, with a Trainer, a Stable-lad, and a Jockey, was bought by the seller for £12,600 in 1951.

Stubbs (1724-1806) was commissioned to paint it by the owner Frederick St John, 2nd Viscount Bolingbroke.

Another version of the painting is in the collection of the Jockey Club in Newmarket.

The previous record for a Stubbs was for Brood Mares and Foals which sold at Sotheby's in 2010 for £10.1m.

Brewer's granddaughter

The previous record at auction for a Gainsborough (1727-1788) painting was £3.6m for A Wooded Landscape with a Herdsman, Cows and a Sheep Near a Pool sold by Christie's in New York in 2008.

The painting sold on Tuesday night, called Portrait of Miss Read, Later Mrs William Villebois (1770s), came from the collection of Cowdray Park, Sussex.

The portrait was commissioned by East End of London brewer Sir Benjamin Truman, who was the sitter's grandfather.

Gainsborough's portrait of Sir Benjamin is in Tate Britain.

Hugh Belsey is a former curator at Gainsborough's House in Sudbury and he is currently writing a catalogue of Gainsborough's portraits for the Paul Mellon Centre for Studies in British Art.

"Mrs Villebois is an exceptional work," he said.

"I am not surprised by the price, but it is not only the fiscal value of great pictures that counts, it is their beauty and the insight they give into the artist and his times.

"He was the only major 18th Century British artist to make an equal contribution to the development of portraiture and landscape painting."