A PORTRAIT by Suffolk born artist Thomas Gainsborough is set to fetch �30,000 at auction.

The painting depicts Catherine Warneford, the daughter of successful drug merchant Samuel Claverley, and it has been passed down six generations since its execution around 1766.

The sitter is wearing a blue dress with a lace fichu around her shoulders and the painting style is typical of Gainsborough’s technique in the 1760s.

It is thought the painting was commissioned to mark the sitter’s status as an heiress who would acquire her father’s estates in London, Surrey and Sussex.

Gainsborough was born in Sudbury and was the youngest son of John Gainsborough, a weaver and maker of woollen goods.

He started drawing at an early age and studied art in London in 1740 where he soon became associated with William Hogarth.

In 1748 he returned to his home town to paint portraits before moving to Ipswich to fulfil commissions for local merchants and squires.

One of his most famous work is an oil on canvas portrait of Mr and Mrs Andrews which hangs in the National Gallery.

Director of the Old Masters department Andrew McKenzie, said: “It is incredibly rare for an unknown painting by such a well-documented artist as Gainsborough, to emerge on the open market and it is a truly exciting moment when a discovery like this is made. The Gainsborough is one of several important paintings in the upcoming sale.”

The painting will go under the hammer at Bonhams Old Master Paintings in New Bond Street, London, on July 4.