Top Shakespearian actor Colin Firth has revealed how he was blown away by a remarkable performance by his new Scots co-star - a learning disabled actor making his TV drama debut. Screen heart-throb Firth, who has worked with some of Hollywood's finest including Ralph Fiennes and Willem Dafoe, described David Brown's debut as "sheer perfection". The 38-year-old amateur actor from Edinburgh was filming alongside Firth for Donovan Quick, a highlight of the BBC1 Scotland festive season, aired on December 28.

    "There is something fantastically pure about his performance," Firth said. "It is very unusual to see that in a piece of storytelling like this. He is delightful."

    In the drama, Firth stars as a mysterious nobleman who briefly enters the lives of a family of pathetic basket cases headed by alcoholic landlady Katy Murphy. He befriends her dim-witted brother Sandy, played by Brown, who can no longer go to school because a multi-national transport company have changed the routes. Donovan commandeers an old coach and suddenly the pair are in business in a David vs Goliath struggle against the big transport boys.

Lifetime opportunity

    For David, who has a learning disability, the chance to act alongside Firth was an opportunity of a lifetime. "I loved every minute of it," he said.

    But Firth, who has just finished filming a Hollywood adaptation of Bridget Jones's Diary with Hugh Grant and Renee Zellweger, confessed he has a soft spot for the Scots film and its brilliant co-star. And critics were so stunned by Brown's performance, they took him for a trained actor. "It's not naive at all to think that of David," added Firth.

    "I have spoken to a lot of people who have not been sure. What he has done and why it is great that he did it was that he didn't play a disability. "He didn't have to do that. Nobody was in front of a camera trying to pick up an award for being learning disabled. "He played a guy. He played emotions. He was just playing a human being."

    Brown's big break came when Donovan Quick director David Blair spotted him rehearsing a performance of La Boheme with an Edinburgh drama group. Brown explained: "The director gave me the part after I did a reading for him. "I'd never been on a film set before and everything was new to me. Having Colin there, supporting me, gave me confidence. "He was great at giving me acting advice."

Firth, 40, who has a huge following since his screen performance of Mr Darcy in Pride and Prejudice, said he also learned a great deal from working with David. "He was chastening for the rest of us in his diligence and all his resilience," the experienced actor explained. "Because it was a short shoot but very work intensive, tempers get frayed. You get worn down at the end of a long week of 14-hour days.

"We are standing in the freezing cold and you look across and David was the one that had the most energy and willingness to keep working. "He loves acting. He is full of enthusiasm. I kept asking myself to what extent does he understand the story we are telling. How much does he understand of what we are dealing with here and why he is chosen for the part? "I didn't know or understand David well enough to be able to answer those questions."

A cheeky dig at real-life

A major appeal for Firth in making the film, which was shot in Glasgow, was the privatisation of the country's transport network. The bully boy-style tactics adopted by the big multi-national Windmill Transport in Donovan Quick are said to be inspired by the rise of the Stagecoach company owned by Brian Soutar and Ann Gloag. Scriptwriter Donna Franceschild, a committed socialist, has written with rattlesnake venom the greed-obsessed methods deployed by big company bosses to try to run the little guy off the road.

Firth said: "I felt things about the script. You can apply it very, very specifically, probably uncomfortably specifically right down to a specific transport company. It's very cheeky."

As if the stunning confrontation between the multi-national firm and the rickety coach operated by Donovan Quick and Sandy wasn't enough, writer Franceschild rams home the point. A Gloag-lookalike - right down to the fashionable piping on her jacket lapels - is the head of the transport empire.