If art promotes healing then the spirits of elderly psychiatric patients in one London hospital should be enlivened by a series of giant paintings from the veteran children’s illustrator Quentin Blake. In one, a plump lady makes up her face in a mirror held by the beak of an obliging crow; in another, a nimble pair of pensioners dance to music pumped out by a band of ageing rockers.

Around the walls, more elderly people are perched in the branches of trees, reading, eating or resting beneath them — or swinging from one to another. Some are joined by their grandchildren; all look as if they are enjoying the liberations of old age. Sixteen of these joyful, humorous pictures are now installed in Kershaw Ward at the South Kensington and Chelsea Mental Health Centre, and Blake is working on 19 smaller ones to decorate individual bedrooms.

This is the first time the 73-year-old Children’s Laureate has taken the elderly as an audience, but though he has spent most of his prolific career concentrating on youth — notably illustrating the stories of Roald Dahl — he has always excelled at eccentric old people: “It’s like drawing motor cars,” he says, “a slightly older, more bent model has more visual appeal. It’s quite hard to draw a handsome young man.” He thinks elderly people probably live a kind of parallel life in which they are more mobile than they really are — hence pictures of grannies juggling and swinging from trees: “What you hope is that the pictures are sort of energising.”

Catering for over-65s with depression and dementia, the Kershaw ward previously suffered from the gloomy decoration and poor lighting typical of institutions of its kind. Dr Nick Rhodes, a psychologist, recalls how bad he felt when examining a suicidal patient in a bare, soulless room at the centre. “I was struck by the madness of trying to treat people for depression in depressing little clinic rooms,” he says. “It seemed insane.”

With the art consultant Stephen Barnham, Rhodes set up the Nightingale Project, commissioning work for exhibitions in the centre’s outpatient department and using the proceeds from sales to fund permanent pieces for the building. When Eric Craig, manager of the centre, approached the project with a brief — “We wanted art that would give a positive image of ageing rather than just the usual flowers and nice landscapes,” — they suggested Blake: “

His drawings are so full of wit and humanity,” says Barnham. “Who better than him to deal with the fraught subject of old age?” On Blake’s mind as he set to work was his brother, ten years his senior, who lives in an elderly care home in Scotland. “I have visited him there, so I have the other view,” says Blake. “It is a dullish place, though very well run. I hope to be sending them some of these pictures.”

The Kershaw pictures are facsimile prints, enlarged from original drawings, which can be reproduced to cheer up other places.

With the pictures hung and gallery-style lighting installed, few traces remain of the ward’s old dreariness. Walking in, one is struck by its bright but calm atmosphere and smiles on faces. Craig claims that the work has lifted the spirits of patients and staff. “It stops people in their tracks,” he says. “Patients find it fun, something they can engage with. A lot of people under- estimate the impact of environment, especially where people are staying for a long period of time.”

Next door, the Chelsea and Westminster Hospital has had an active and successful arts programme since it opened in 1993. While some in the NHS, particularly those who handle budgets, are still sceptical, this hospital can now point to scientific data showing that an attractive, stimulating environment aids healing. A three-year study here demonstrated that bringing visual and performing arts into the hospital had measurable physiological effects, reduced the amount of drugs consumed and shortened hospital stays. Other research shows that art can reduce agitation among dementia patients and improve communication skills.

Blake himself is cautious about predicting the effect of his work on patients. “I don’t know enough about the mental problems that these people have,” he says. He overheard one elderly lady on the ward rubbishing the paintings almost before they were hung: “She was marvellously negative. She said: ‘I’ve no idea what these are for, I mean nobody wants to look at them and you can’t understand what they are’.” But he is delighted to hear that other patients have described the work as “a joy”. “It’s worth it already,” he smiles.

At lunchtime, patients sit together underneath an 8ft-long picture of elderly folk eating and drinking with gusto while a bird flies off with a piece of spaghetti in its beak. “The pictures attract me so much,” says one Alzheimer’s sufferer, and points at a jolly man reclining on a tree branch. “He reminds me of my grandpapa.”

Another lady describes the work as “terrifically good: the best improvement here. It was terribly empty before, militarised if that’s the expression.” A third observes: “There’s a lot of conversation in them if somebody takes the trouble to make any.” There are plans to use Blake’s work as a starting point for therapeutic discussion.

Staff benefit too, says Dr Jose Catalan, a consultant psychiatrist who works at the centre: “If we are surrounded by nice things, feel happier and have more smiles on our faces, we may deliver better,” he says. Another doctor at the centre, Claire Smith, is certain that art has had an impact on patients and their relationship to the building: “And using an artist as well known as Quentin Blake makes it feel important, not just a place that nobody cares about,” she says.

You might think that this sort of medical endorsement — plus savings made on shorter stays and smaller amounts of medication — might persuade NHS managers of the economic benefits of buying art. Not so, says Lara Dose, director of the National Network for the Arts in Health. “We live in a culture where we still apologise for spending money on the arts. There’s an outrage when a hospital spends money on a sculpture to mark its entrance. Until we can change that, we still have a bit of a hill to climb.”

The Quentin Blake originals are on show at the South Kensington and Chelsea Mental Health Centre until September 8. Details at www.nightingaleproject.org