When a young tree surgeon called Richard Vallis responded to a poster by learning disabilities charity, The Action Group, it set in motion a chain of events that not only changed his life, but changed the cultural landscape of Edinburgh forever. It was the late 1970s, and The Action Group, set up in 1976 by parents of children and adults with learning disabilities, were looking for volunteers to work with them.

Lancashire-born Vallis had recently moved to the city, and, wanting to meet new people in the place he still calls home, thought he'd chance his arm. Today, Lung Ha's Theatre Company, which was formed as a direct result of Vallis' involvement with The Action Group, celebrates its thirtieth anniversary as one of the UK's leading exponents of inclusive arts working with performers with learning disabilities.

While an informal celebration will take place next week, this weekend sees the opening of Lung Ha's latest production. Thingummy Bob is a new play by Linda McLean, which looks at the effects of dementia on an ageing disabled man. Coming at a time when many of Lung Ha's most senior members are moving into a new demographic, Thingummy Bob, which forms part of the Luminate festival of creative ageing, is an apt way for Lung Ha's to move into middle age.

“I wanted to write a comedy in the widest sense of the word,” says McLean. “My own-step-father had Alzheimer's, so I know it can be a very challenging condition, but he could also be very funny.”

McLean was first approached to work with Lung Ha's by the company's current artistic director, Maria Oller.

“Some of the company members are about the right age, ” she says, “and I thought Linda could do something amazing with the subject.”

While the responsibility of writing the play laid with McLean as it would with any other company, she found the show's development process quite different.

“It's a much longer rehearsal period,” she says, “and I had my hands on the actors from very early on, so I knew who I was writing for. But Lung Ha's seems to me to explore two things. One is inclusivity, and the idea that everyone is creative. The other is that art can cause happiness.”

This ethos was in place from Lung Ha's first ever show, which was born out of Vallis' work with a six-strong drama group at a day centre in Restalrig.

“It was something I'd never done before,” he reflects today. “I'd done a bit of mainstream youth work, but I'd never worked with anyone with learning disabilities before. It was something to take me out my comfort zone.”

Alongside his work with The Action Group, Vallis became involved in a burgeoning community arts scene that existed in Edinburgh in the mid 1980s. He was particularly attracted to the large-scale community plays at the Stockbridge-based Theatre Workshop. It was here Vallis met drama worker Pete Clerke, who would go on to co-found the leftfield Benchtours theatre company.

With some of Vallis' drama group suggesting they become more ambitious in their endeavours, Clerke visited Restalrig, where the group had been developing a short piece inspired by high-flying cult Japanese TV series, Monkey. As Clerke remembers it, the piece presented to him was “the most surreal ten minutes of theatre I've ever seen, before or since.”

With Clerke on board, the group spent the next six months developing what would become Lung Ha's Monkey, a full-length multi-media extravaganza performed over three nights at the old Cowgate-based Wilkie House venue as part of the then Edinburgh District Council's Spring Fling community arts festival. Utilising slide projections and sculpture as well as performance, Lung Ha's Monkey showed what could be achieved with determination and a civic will that seems to have vanished now.

“It was amazing,” Clerke recalls. “Nothing on that scale had been done before with people with learning disabilities, and the energy in that hall after the first performance blew the roof off. There were a lot of naysayers who said we couldn't do it, but we proved them wrong.”

As word spread, so the company grew, and Lung Ha's followed their debut show with a large-scale take on Homer's The Odyssey. Since then, Lung Ha's have produced more than forty shows, which have seen directors such as Andy Cannon, John Mitchell, Michael Duke and Annie Wood oversee work penned by the likes of John Harvey, Louise Ironside, John Binnie and Grace Barnes. Clark Crystal was appointed as Lung Ha's first full time artistic director in the early noughties, while under Oller's tenure, the company has co-produced shows with Drake Music Scotland, Grid Iron and Stellar Quines theatre companies. Lung Ha's most recent productions include a version of Antigone by Adrian Osmond, an adaptation of Jules Verne's Around The World In 80 Days by Douglas Maxwell, and a reinvention of Jekyll and Hyde by Morna Pearson.

“I think Lung Ha's is in a really interesting postion just now,” Oller says. “In the five years I've been with the company, we've tried to train our actors as much as possible and become as professional as possible. There's a short course now at the the Royal Conservatoire of Scotland for actors with learning disabilities, so things are changing all the time.”

These days Clerke is based in Winchester, where for the last six years he has worked with Blue Apple Theatre, a company similar in ethos to Lung Ha's.

“There is such a demand,” he says. “Companies like Lung Ha's and Blue Apple provide a lateral way of increasing people's life skills and social skills, and if you can get people feeling really good about themselves by performing, the effect on their everyday lives is enormous. But it's very important that Lung Ha's is an arts company first.”

Vallis, who lost his leg to cancer several years ago, still works with people with learning disabilities, , and remains Honorary President of Lung Ha's, who he sees as confounding all expectations of what the company could achieve.

“People saw what we were doing could be done,” he says, “and took it to their hearts.”

Lung Ha's immediate plans for the future include Silent Treatment, a new play by Douglas Maxwell which will not use words at all, but which will be pulsed by a musical score composed by M.J. McCarthy. In the longer term, Oller expresses ambitions for the company to have its own rehearsal space. This would give them the flexibility to set their own working schedule, and would also allow the cast to work on set from the beginning of the rehearsal process.

“We'd also like to do more collaborations,” Oller says, “particularly in terms of collaboratiions betweeen disabled and non-disabled casts, just to blur those lines and step over a border a little.”

McLean for one is a fan.

“I'd love to write a big show for Lung Ha's,” she says. “The actors are so energising. There are no quiet silences after a first read-through when you're wondering what people think. No-one's holding back.”

Vallis too remains as enthusiastic as ever for the company he kickstarted into life.

“I'm still completely surprised and amazed,” he says. “but I'm also proud of all these fantastic shows that the company are putting on. For a crazy idea that we were told wouldn't work, I think we've done rather well.”

Thingummy Bob, Traverse Theatre, Edinburgh, October 29-31; Eden Court, Inverness, November 3; Platform, The Bridge, Glasgow, November 5-6.

www.lungha.com