A rare collection of equestrian paintings will open Bonhams’ Old Masters sale on 8 December. Eight works by James Seymour (1702-1752) are expected to fetch more than £150,000 as they go under the hammer next week.

The collection, which had not been seen for many years, belonged to the late David Astor, a former editor of the Observer, and was hung in his Oxfordshire home until the house was sold earlier this year. Astor probably acquired Seymour’s works when he bought Manor House in Sutton Courtenay, Oxfordshire, from the previous owners, Captain Harry Lindsay and his wife Nora, in 1945.

James Saymour lived in the early 18th century and was the precursor of the line of British equestrian portraitists that culminated with George Stubbs and Sir Alfred Munnings. The son of a wealthy London banker, he gambled away the family fortune and it was probably his skills at painting which saved him from ruin, because thoroughbreds were being introduced to racing in the early 18th century and equestrian portraits were much in demand.

Seymour is best known for his paintings of racehorses and hunters, although the Astor collection also includes two unusual canvases depicting a hound and a bitch, which were probably commissioned by an owner who wanted a memento of his favourite dogs.

The hound and the bitch, which measure 12 x 14 inches each, are sold in a single lot and are expected to fetch £15,000 to £20,000. Many of the collection’s paintings are extraordinarily small — A bay racehorse at exercise is just 101/2 x 12 1/2 inches — but rich in details.

Seymour’s portrait of Childers with a jockey up shows an elegant racehorse with long, agile legs and does justice to the colt’s reputation as “the fleetest horse that has ever appeared in the world.” The largest work of the group is A chestnut hunter with rider up, which measures 361/8 x 357/8 inches. Expected to fetch £40,000 to £60,000, it is very rare because it is an oil on panel, which is a support Seymour hardly ever used.

Seymour’s works are complemented by two other equestrian paintings, which also belonged to the Astor collection. A portrait of Fairy — of English school and dating from circa 1768 — is expected to sell for £8,000 to £12,000, while an early pair of racing scenes by Flemish painter Peter Tillemans (1684-1734) are estimated at £15,000 to £20,000. Tillemans’ works are thought to portray the paddock and course at Newmarket, where the artist lived, although Bonhams say that “the geography of the area has been rather freely interpreted.”

The Bonhams Old Master Paintings auction will take place at their New Bond Street saleroom on 8 December. For further information, visit www.bonhams.com or call 0207 447 7447.