The auctioneer had been called to the house to value its furniture. But the owner also had some other things for James Braxton to look at.

She wanted to know if the contents of piles of big black rubbish sacks which had been stowed in the loft of her home in Eastbourne for years were worth selling.

Inside was a haul of previously-unknown material relating to the most famous artist to ever live in Ditchling, Sir Frank Brangwyn.

Sue Thomas, James' colleague, said: "The amount of material was astonishing. They kept bringing more and more bags in for us to look through."

The collection includes hundreds of articles, including photographs, books, letters, etchings and personal belongings given to the late Edgar Peacock, the son of Brangwyn's long-serving housekeeper Lizzie Peacock.

None of the material has been seen in public before.

Painting valuer Sue said: "Brangwyn kept himself aloof from Ditchling life and was considered by many to be a recluse. But some of the photos that have been unearthed prove he was quite an extrovert.

"There are hundreds of him posing for his paintings, including one of him dressed up as Christ."

Edgar grew up in The Jointure, the house in Ditchling where Brangwyn spent his last 30 years before his death in 1956, and was unofficially adopted by the artist after his own father died in the First World War.

Sue said: "Many of the books have been inscribed by Brangwyn to Edgar but he has used his full name. Although he was a father-figure, it is obvious they still had a kind of master/servant relationship."

Gems in the collection include a gold-topped malacca cane used by Brangwyn's invalid wife Lucy, who died in 1924, a letter from Sir John Betjeman and a copy of Brangwyn's biography with critical notes by the artist scribbled in the margins.

Edgar Horn, auctioneers in Eastbourne, will divide the collection into 40 lots to be sold on September 20.

An auction catalogue is available from today.

Sue is reluctant to put a price of the biggest Brangwyn collection her firm has ever dealt with but conservatively estimates about £3,000.