The Walled Garden in Perth: A refuge from the stresses of the outside world

• Photographer Graham Miller, inset left, has created a series of pictures of the people working in the Walled Garden. Picture: Complimentary/Graham Miller

Yellow roses are in bloom, fruit is already visible on the damson trees and the gentle hum of bees can be heard among the bedding plants and herbs. Here and there, men are toiling: watering the hanging baskets, weeding the vegetable patch or running a strimmer along the edge of a lawn. Everywhere, there are signs of new growth – but it's not just plants that are being nurtured in this small patch of land at Pitcullen House in the grounds of the Murray Royal Hospital. The garden – together with its caf, art studio and joinery – provides work for around 40 people with severe and enduring mental health problems, giving them a chance to lead productive lives, free from the pressures many full-time jobs would bring.

People who arrive disempowered, isolated, and uncommunicative blossom in an atmosphere of professional guidance, mutual support and, it seems, almost relentless ribbing. "When you meet someone who would hardly say boo to a goose, and then, a while later, they are slagging you off something terrible, that's very rewarding," says joinery supervisor Dave Harris.

Despite its almost preternatural tranquility, the walled garden is full of larger-than-life characters: there's Euan Stewart, once so cut off from the world he refused to answer the telephone, now clutching a Twilight Saga CD like it might be hatching an escape plan, while holding forth on the joys of a trip to a Forbidden Planet shop; Cully, who lives to wind up the staff; and Tommy Wylie, whose brightly optimistic art studio paintings are balanced by the more sinister drawings on the back of pay packets which greet the unsuspecting visitor in odd spots around the garden (an expression of the other side of his "split personality", he later explains).

All say the centre, run by Perth and Kinross Association of Voluntary Services, has handed them a lifeline, giving them an outlet for their talents, a forum for friendship and – in Cully's case – enabling him to give up drinking before it killed him.

But with depression still very much a taboo subject – and the Cumbrian massacre raising fresh fears about the link between mental illness and violence – the workers are well aware that beyond the physical and emotional shelter of the enclosed garden, they can be regarded with suspicion and occasional hostility.

Next month, some of them will feature in a photographic exhibition which aims to tackle the stigma that surrounds mental illness. For the last year, they have allowed Perth-based businessman and amateur photographer Graham Miller to snap them at work.

The result is a collection of captivating, poster-size images printed on aluminium composite material, which will go on display at the Birnam Arts and Conference Centre in Dunkeld on 3 July. "Now I know these people, I find it quite sad. I go into town in Perth and I'll be walking around and you see them sitting in the corner of a coffee shop or shuffling around in shopping centres and everyone is giving them a wide berth, they're totally invisible because they look a bit odd," says Miller, 48. "I have very deliberately made the photos large, so they're really dramatic. I'm taking these guys, who rarely get their photos taken, and making them huge to put them into people's faces, to say these are important people, they have to be taken seriously like every other human being.

"But it's not just the way other people view them, that's the problem, it's the way they view themselves. I have heard mental health campaigners saying they begin to believe their own bad press, they start to think that's their place in society; that they shouldn't have any ambition beyond what they're doing, that they should keep their heads down – I want to encourage them to see themselves in a different way too."

Miller looks after the commercial interests of a US company specialising in scientific equipment. He became interested in mental health issues after joining the Samaritans several years ago. "I guess it became clear to me there are people out there in the community who are not as well-supported as they might be," he says.

His contact with the Walled Garden began with a speculative visit after he received a donation for a charity trek to Vietnam from a woman who worked in the caf. But it was what happened when he arrived that convinced him to engage in a long-term project with the workers. By sheer chance, one of the first people he met was Ian Watt, who, it turned out, had studied chemistry with him at Paisley Technical College almost three decades earlier.

"Ian came up to me and said, 'Goodness Graham, you've filled out,' in that kind of straight forward way many of the guys have. But that sense that we had started out together and that our lives had taken such different paths was really quite striking."

Watt has been working there for 16 years, now. "I tried indoor work for a while, but I didn't like it," he says. He describes the work as "a steadying influence": "The good thing is you know you can take time away if you are ill, and the job will still be there for you when you get back."

The Walled Garden caters for people with long-term mental health problems from severe depression to bipolar disorder to schizophrenia. The items the workers produce – fruit, vegetables and flowers in the garden, wooden benches, tables and planters in the joinery and art works in the art studio – are sold, with the garden doing a roaring trade in wreaths at Christmas.

"It simulates work, but it's safe, there's no pressure. There's very gentle discipline, the workers come in on time, they have lunch and breaks. Some move on to other employment and some don't," says manager Mike Walsh, who successfully fought NHS plans to scrap the nominal "incentive payments" workers receive earlier this year. "Work is ennobling, it gives you self-confidence, it gives you comradeship, it gives you a place to be. If you balance it against sitting in the home watching daytime television, it's an easy win."

The workers use self-deprecation and humour as a buffer when talking about their problems. An inquiry into the state of their health is likely to be met with the dry response: "I'm no well. I've no been well since 1983." But it's clear they have been very seriously affected. Most of them have been in-patients at some time and at least one of has received electroconvulsive therapy (ECT).

"Sometimes the experience of going into hospital can leave people with more problems," says Susan Scott, development worker with mental health charity Plus Perth. "People come out and you'll hear them saying, 'I can't do anything' or 'I'm useless', or they might not say it but they're conveying it, because they've had their decision-making taken away from them."

Despite being initially cautious, the workers agree being involved in the photographs has been a worthwhile experience. "I wasn't sure at first, but when I saw the final results I was quite impressed," says Watt.

For Scott, the significance of the exhibition lies in its potential to raise awareness: "Stigma is one of the biggest issues for people who suffer mental illness and are just beginning to become unwell, because often they don't tell anyone, and something that might have been more easily helped, becomes a serious problem.

"Graham showed me his images and spoke of his idea about trying to promote value and dignity and all the things that quite often get lost when you have a mental illness, and we're totally behind him."

Back at the garden, excitement about the exhibition launch – to which they've all been invited – is beginning to build. Miller is determined that, however rewarding it has been, the project won't end when the exhibit closes. Instead, he hopes to help the workers produce a book of the images, and teach them to take photographs, using traditional film cameras rather than digital.

"One of the men told me his father had a darkroom and he remembers the smell of the chemicals," Miller says. "It's a magical process, when you rock the tray backwards and forwards and see the image come up."

For the moment, however, the workers are more concerned about getting to and from Dunkeld: a minibus has been arranged and the possibility of a post-event party is being hotly discussed.

"I think what this has done is to hold a mirror up to these people's faces, when they have not been focused or conscious of themselves before," says gardening supervisor Brian Greer. "I mean, one of the guys is so captivated by his picture, he wants to buy it. He thinks he's a wee superstar.

"At the beginning they were saying, 'Why are we the focus of this?' Over the course of the year, they have become more willing to have snaps taken. And now? Well, some of them are practically models."

The Most Important People in the World: Honesty runs from 3 July to 3 August