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The estate had belonged to the late Joseph Hay, a childless bachelor who died intestate some four years ago. The auction house was entrusted with the valuation after Hay’s next of kin were finally traced earlier this year.

“We had to crawl our way through the overgrowth to get into the property. It was a bit of a time warp inside, nothing had really been moved since the property was built in the 1960s,” said Batemans’ managing director Greg Bateman.

The Hays had a compelling family history. Joseph Hay’s father and grandfather had been major-generals in the British Army, while his mother’s family featured several notable navy admirals, and according to Bateman, a captain whose ship had patrolled St Helena at the time of Napoleon’s imprisonment on the island.

The Girtin watercolours, which had survived in “decent original condition”, had no paper trails (unlike other antiques from the property), and were thus believed to have been inherited from a previous generation.

Windsor Forest, a 7½ x 6in (19 x 15cm) landscape of grazing deer among large oak trees, easily surpassed a £400-600 guide to sell to the London trade at £8000.

The other view, a similar-sized watercolour of Bothwell Castle in south Lanarkshire, Scotland, proved less commercial. Against the same estimate, it was taken to £2100 and was knocked down to a different UK buyer.

“The fact that the location was Windsor is the only reason why we think it made the extra money,” said Bateman.

Elsewhere from the estate, a slightly foreboding drawing of London Bridge engulfed with birds by William Lionel Wyllie (1851-1931) was given an enthusiastic guide of £300-500. The 19 x 14in (49 x 36cm) dry point etching on paper went to a trade buyer in the north of England who pipped a commission bidder to buy it for £621.