When more than 1,200 sketches, photographs and documents from the studio of Francis Bacon were donated to the Tate in 2004, it was described as one of the most generous gifts the gallery had ever received, estimated to be worth £20m. Now the donor is threatening to cancel the gift, accusing the gallery of reneging on pledges to stage exhibitions of the material. Barry Joule, a longstanding friend of Bacon, had wanted the items to go to the Tate, as it had been the artist’s favourite gallery. Over the years, he kept expecting the Tate to do justice to it with an exhibition, as he says they had planned on accepting the gift. He wrote repeatedly to curatorial staff, asking when the show would happen. After almost two decades of waiting, he has lost patience. Not only is he prepared for a legal battle, but he told the Observer he is also cancelling a planned bequest to the Tate of an important 1936 Bacon self-portrait and nine other Bacon paintings from the same period. Nor will he leave them “a considerable amount of other Bacon artwork, letters, books, tape recordings” that he had intended to leave if the Tate fulfilled “all of the terms and the spirit of the 2004 contract”. Last week, he copied the Observer into an email exchange with the Tate’s director, Maria Balshaw, dating back to 2018. Most recently, on 3 August, he wrote to her: “If a satisfactory conclusion is not reached … by October 2021 over the exhibition terms of the Tate-Joule contract, I shall most seriously consider taking the legal path for resolution of this very frustratingly long outstanding troubling matter – one which clearly means I shall seek the complete return of this my 2004 Tate Francis Bacon studio donation. And so the matter may ultimately be decided in the courts.” Joule’s gift had included Bacon’s dramatic oil study of the head of William Blake, the poet and painter. He argues that a couple of display cases in the archival exhibition area, which showed some of his letters from Bacon and his photographs of the artist some years ago, did not do justice to the collection. He disputes the Tate’s claim that the terms of the contract to catalogue and exhibit the works have been fulfilled. He wrote to Balshaw: “Where and when exactly did this take place?” He acknowledges that his 2004 donation occurred before Balshaw became Tate director in 2017, but says that the “contract” is now her responsibility. He told her: “When Tate curators … saw my Bacon archive long before my Tate donation was completed, they all suggested an exhibition at the Tate … [Then] director Sir Nicolas Serota in 2003 assured me a month before the contract was signed this would be the case and within three years of my donation. Yet, as time passed, I was continually met with silence, ignored or just fobbed off …” In its 2004 gift announcement, the gallery noted: “Tate will undertake to study, photograph and catalogue the collection over the next three years, before displaying these items and making them available for loan.” Bacon is widely regarded as the greatest British painter since JMW Turner, although he never imagined that his 1969 portrait, Three Studies of Lucian Freud, would sell for £89m in 2013. He once said: “When I die, my paintings won’t be worth anything.” Joule had lived near Bacon’s studio in London. In 1978, Bacon saw him repairing a neighbour’s television aerial and invited him in for some champagne. They struck up a friendship that continued until the artist’s death in 1992, after he had a heart attack in Spain. There is a poignant paragraph in Joule’s latest email to Balshaw: “On April 18 1992 … I dropped Francis Bacon off at Heathrow airport, this only hours after he had given me the huge pile of art and material … During our long parting embrace in the busy departure lounge, he spoke directly into my ear, ‘You will take care of things when I have gone.’ Naturally I promised to do so and thought at the time he meant finishing off some handyman chores … whilst he was away in Spain, never imagining for a second that this would be the last time I or anyone else in England would ever see him alive.” There were initial questions from the Bacon Estate about the material’s authenticity – prompted, Joule believes, after he refused a 1998 request to donate the material to the Bacon Study Centre at the Hugh Lane gallery, Dublin. But the Tate accepted the gift and, last month, Balshaw wrote to Joule that the material “sheds unique light on the working habits and environment of one of the leading painters of the last century”. She reiterated the gallery’s gratitude and assured him that material had featured in various displays and was “very much appreciated”. But Joule is all the more frustrated because he says the Tate’s response contrasts so dramatically with that of a French museum – the Musée Picasso in Paris – to which he donated 80 Bacon drawings. Bacon began to paint in around 1930, inspired by a Picasso exhibition. Joule told the Observer: “All these donated drawings were exhibited in a large Bacon/Picasso painting exhibition held at the Musée Picasso in 2005. The Musée Picasso published a handsome separate catalogue … The exhibition was a huge success and, two years later, the French government awarded me the highly sought-after Chevalier des Ordres des Arts et des Lettres – the French equivalent of a knighthood.” He added: “In 2008, the Tate held a large Bacon exhibition. Not a single item from my 2004 Tate donation was included.” If he withdraws the Tate gift, he will donate it instead to a French museum. The Tate said: “We have proposed a meeting with Barry Joule in September.” The Bacon Estate declined to comment.