This Bob and Roberta Smith-curated exhibition has both an intriguing name, and unusual aims.

Artworks can often have misleading names. Would you guess that The Physical Impossibility of Death in the Mind of Someone Living is actually Damien Hirst’s (in)famous shark in formaldehyde, for example? Or that Rene Magritte’s The Son of Man is a painting of a well-dressed chap with an apple for a face? But Snail Porridge, the title piece from a new exhibition of art made by inmates, is rather literal: porridge stands for time inside, snail because the time goes so slowly and Snail Porridge because, well, the painting is a picture of a snail slithering by some psychedelic porridge. Perhaps more abstractly, it is a point about the twisted indulgence of modern art itself, akin to a Heston Blumenthal meal – who, of course, has a dish called Snail Porridge.

This painting is just one of dozens on display at the Castlefield Gallery as part of an exhibition by the Koestler Trust, a charity that promotes the rehabilitation of inmates through art. The event (9 May-15 June) is curated by Bob and Roberta Smith (the artist moniker of Patrick Brill), who paints slogan and poster art pieces that promote socially progressive ideas. The submitted works – including paintings, music and writing from prisons, secure hospitals, secure children’s homes and by people on probation – have been broken into four groups:  remembered landscapes, art as escape, well-being/inner peace and art as a product of prison life. “They really have something to say and are puzzling it out on canvas,” says Bob, who has created a piece to accompany the exhibit. “It’s almost like 14th Century revelatory art in its quality and intensity.”

Porridge stands for time inside, snail because the time goes so slowly

Bob believes there is something wholly different about the approach behind the artwork in this exhibition. “When I am making art it can feel like I am speaking directly to the art world,” he says. “But these works are a direct cry of the artist to the public…and I find that very liberating.” Further, the meticulous nature of the works came as something of a surprise. “In modern art attention to detail isn’t always important, but here the works are so meticulous and thoughtful,” he argues, and it is clear from his voice just how impressed he is by the quality of the canvasses, “And not only that, you know the artist actually made the work rather than just someone in the artist’s workshop.”

The Koestler Trust itself was founded by novelist Arthur Koestler, whose works such as Arrival And Departure dealt with themes of justice, punishment and self-awareness. He became interested in the intellect of the incarcerated, and set up the first Koestler Awards in 1962 to help reduce recidivism and encourage personal growth. Bob was so impressed by the trust and their work that he has attempted to recreate the atmosphere of their Wormwood Scrubs HQ at the Castlefield Gallery, using the same paint scheme and hanging artworks in a similar floor to ceiling fashion. “I started work in October and was amazed by the Trust’s building. It’s bright yellow inside, with work pinned up from floor to ceiling, piles and piles and piles of art…an inspiring space,” he remembers.

Bob is taking part in the Royal Academy Summer Exhibition for the first time this year, but will not soon forget the time he has spent with the Koestler Trust. “I used to be a sceptic, but art really can be therapeutic,” he says, before concluding: “and just because someone has done something bad in the past doesn’t mean they don’t have something important to say.”