Even after he found fame as one of the most important 20th-century British artists, Leon Kossoff never got over the distress of losing 14 paintings and six drawings in an unsolved theft. A much-loved portrait of his mother was among pictures that were stolen from a lorry transporting them from London to Italy in 1972, with some speculating that the mafia was responsible. Until his death two years ago, he was obsessed with being reunited with them one day, but he never saw them again. Now art historians hope that the inclusion of those works in a forthcoming major publication will jog people’s memories and finally lead to their recovery. The images of the lost works will feature in a definitive study, Leon Kossoff: Catalogue Raisonné of the Oil Paintings, to be published in September. It is edited by Andrea Rose, former director of visual arts at the British Council, who curated Kossoff’s exhibition at the 1995 Venice Biennale, when he represented Britain. She was also a close friend of the artist, an intensely private man who died in 2019, aged 92. She told the Observer: “He was hugely upset by the theft.” Kossoff, the son of a baker who grew up in east London, was among figurative painters such as Lucian Freud and Frank Auerbach who became part of the School of London. Inspired by the old masters, he captured urban life in expressionist paintings, with swathes of thick impasto paint and a sombre palette. He once said: “London, like the paint I use, seems to be in my bloodstream.” His subjects included postwar bomb and construction sites, crowded swimming pools and portraits of family and friends. Despite major exhibitions at the Tate and the National Gallery in London, as well as international shows, he never forgot the stolen works created when he was establishing himself. Several were important paintings and had been shown at his solo exhibition at the Whitechapel Gallery in London, before being sent to his first solo exhibition in Italy, at Galleria del Girasole in Udine, in August 1972. The lorry got as far as Rome – only to disappear after it had been left overnight in a car park, with the driver staying in a nearby bed and breakfast. Rose said: “The following morning, the truck had vanished, and was later found 17 miles away … The locks on the back door had been smashed, and all of the cardboard cases had been opened. All of Kossoff’s paintings and drawings had been stolen. There were a few other items in the truck, among them a bronze sculpture and a 16th-century painting. None of these had been removed.” She added: “There has been some speculation about what might have happened to the paintings, involving the Italian mafia in London, but none of this is provable. At the time of the theft, Kossoff was a rising star of the British painting world, but his works had not been shown in Italy before and he therefore was not a well-known name in Italy.” The paintings would have been particularly heavy, partly because Kossoff was using lead paint at the time. It would have taken two men to carry them. Another truck must have been involved. Not one of the works has been seen since, despite investigations by the police and insurers. Apart from the portrait of his mother, Woman Seated in an Armchair, which was painted in 1965, the other stolen works include Nude on a Red Bed, Winter 1970-71, part of a series of paintings of his wife Peggy – described by Rose as an “unsentimental but very affectionate” image. Also missing is his Portrait of David, Summer 1970, a tender depiction of his son, who was a teenager then. David said of his father yesterday: “The mysterious disappearance of these paintings and drawings – in particular the large painting of his mother, which he thought was among his best works – disturbed him throughout his life.” The Italian exhibition had been organised by Lou Klepac, who went on to become curator and deputy director of the Art Gallery of Western Australia. He remains puzzled by the theft as Kossoff was not known in Italy and, even in Britain, his works changed hands then for only a few hundred pounds. Now they fetch seven figures. He said: “Today, if you sent Kossoff paintings [somewhere], you would need an armed guard. Then, Leon’s work was not popular with anybody.” He wonders whether the thieves, perhaps linked to the mafia, thought the truck had valuable goods, only to be disappointed. Most of the stolen works had been photographed before they disappeared, enabling them to be reproduced in the catalogue raisonné, which will be published by Modern Art Press on 30 September. The publication coincides with a major retrospective exhibition at Annely Juda Fine Art, London, which will travel to New York and Los Angeles in early 2022.