Watercolour by Turner discovered in Scottish mansion

Auctioneers asked to clear the house of a civil servant in Scotland found a painting by J M W Turner tucked behind a door. The work is the only recorded watercolour by Turner of York and stems from the time at the end of the 18th century when the artist travelled to the North of England.

Christie's is selling the picture in London on Thursday and expects that it will fetch up to £100,000.

The painting,On the River Ouse with a View to York Minster in the Distance, was found by the auctioneer Thomas R Callan while clearing the mansion in Ayrshire of the late Theodore Bruen, a civil servant and antique collector. Mr Bruen bought it in Glasgow in 1956 but his descendants were oblivious of the importance of the work, which hung on a wall behind the living room door.

Michael Callan, the auctioneer who spotted it, said: "I'm sure we will never come across another Turner ... You never ever imagine you would encounter one through work."

The painting stems from one of the most important periods for the artist, when he developed new ways of recreating space, light and atmosphere on paper and canvas.A Christie's spokesman said: "It enables us to see the intricate and subtle process whereby he built up the rich, expressive washes in which he could convey his new understanding of the grandeur and emotional intensity that we find in the world, both natural and man-made."