Turner rarely painted royal palaces

The painting, which was rediscovered in a private collection in 1989, was sold for �478,000 at Sotheby's in 1990.

Turner's Heidelberg with a Rainbow currently holds the record for a British watercolour sold at auction. It was bought for �2m in 2001.

Sotheby's expect Hampton Court Palace to fetch between �400,000 and �600,000.

Royal portraits

Only three paintings have beaten the watercolour record since the last sale of Hampton Court Palace - John Frederick Lewis' Lilium Auratum, Heidelberg with a Rainbow and another Turner work, Mont Blanc from Fort Rock, Val D'Aosta.

Following the sale of Hampton Court Palace in 1859 for what was then the large sum of �168, the painting was largely forgotten for 150 years until its sale 14 years ago.

Other works on offer at Sotheby's Important British Drawings, Watercolours and Portrait Miniatures Sale include Samuel Palmer's Landscape with Peasant Girl Minding Cattle: Evening, which is estimated at between �100,000 and �150,000.

John Constable's portrait Study of a Girl Reading is expected to fetch between �30,000 and �40,000.

A portrait of King Charles II from the family collection of Michael Ireland Blackburne is also on offer.