This 3ft 3in x 2ft 11in canvas by Francis Bacon is one of five mutilated examples going under the hammer at Ewbank’s on June 21. It carries an estimate of £4000-6000.

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This time it comes from Ron Thomas, who became friends with Bacon during his 18 years as a porter, picture hanger, and odd-job man at Marlborough Fine Art.

He frequently ferried paintings from their gallery in Mayfair's Albemarle Street to Bacon's studio in South Kensington, where the artist would often ask him to dispose of canvases or keep the stretchers for his own use.

Thomas visited Bacon at Reece Mews and took his family to the artist's home in Wilvenhoe, Essex, and it is obvious that Bacon felt warmly towards the Thomas family. He sent Mr Thomas a cheque each Christmas to buy treats for the family, wrote Mr Thomas many letters when he was sick in hospital, and once even gave him his old overcoat and a pair of boots, which ended up at a charity shop.

The former porter retired in 1987 and kept the canvases and letters tucked away in drawers at his home - until last month when news reached him of the sale of the Mac Robertson Collection at Ewbank's and of its surprisingly high results.

Now in his 70s, Mr Thomas decided it was a good time to sell.

The selection is not nearly as varied or as large as its predecessor, but does contain six large canvases, five of which the artist mutilated. Though it is difficult to identify the subjects, one example appears to be a portrait with a shoulder and part of the body draped in purple robes, which Ewbank's suggest could very easily have been a portrait of Pope Innocent X. It is estimated at £8000-12,000.

Another canvas appears to depict a woman, possibly one of the frequent Bacon sitters, Henrietta Moraes or Isabel Rawsthorne, and is estimated at £4000-6000. There is one whole canvas on offer, a signed lithograph entitled Study for a Portrait of John Edwards 1986 that was a gift to Mr Thomas from the gallery upon his retirement.

There are also exhibition posters, and numerous signed letters offering insights into the porter-artist relationship, with messages like Will you come down to the Black Boy pub where we had lunch last time?

The collection will go under the hammer on Thursday, June 21.