GAIL Gyi reclines in a rooftop bar in Glasgow, looking every inch the media mogul. Her laptop hums; her BlackBerry buzzes. Without warning, she puts her glass of wine down and points quickly to the street below. "I've just seen a black man," she says. "Over there." I look. It's true. The person in question ambles away, oblivious to a comment that might otherwise appear racist. But as the head of Scotland's only ethnic casting agency, Gyi has a professional interest in such sightings. Her eyes follow the man until he disappears, almost disappointed that he has got away.

Since starting Ethnika in 2004, Gyi has amassed more than 400 clients. She flicks through a folder to reveal people of nearly every colour from almost every walk of life. "This girl is Inuit," she says, "but she had to go back to Alaska." Gyi's clients have appeared in a wide range of Scottish productions. Occasionally they have speaking roles but are more commonly employed as extras. Chances are, if the person in the background is black, Asian or Chinese, they have initially come through Gyi.

"When I first moved to Scotland 10 years ago I noticed there were hardly any black or Asian people on the screen," she says. "Certainly not in shows like Taggart or Rebus. Now, I can sit watching the telly most nights and know that my people are in nearly every Scottish fictional programme"

The company's motto of "source local - act global" seems particularly apt for Gyi. She is the daughter of a Nigerian father, who was sent to the UK by a Scottish Methodist minister, and an English mother, who raised her in Harrogate, North Yorkshire. Her surname - taken from her stepfather - is Burmese. She worked worldwide as an account manager with Trans World Airlines before moving to Glasgow, where she gained a masters degree in international tourism. But it wasn't until working in the office of another Scottish casting agent - "between jobs" - that she finally discovered her vocation.

"Someone rang us up asking for 200 Japanese extras for a documentary on Kublai Khan," she remembers. "My boss said it was impossible, but I told them we could do it. I knew there was a Japanese Nissan factory in Sunderland, so I just made one phonecall and got everyone we needed. From that point on, I realised I could do this job with my hands tied behind my back."

She now functions, she says, as a "one-woman army" and a professional "pain in the arse," lobbying television executives and casting directors across Scotland for more diversity on our screens. If she sees someone of an ethnic minority background in the street she will offer to represent them. If they agree, she will likely sign up their relatives and friends. Fittingly for an ex-rugby winger with the West of Scotland ladies team, her manner is forceful, and relies on instinct as much as experience. "There's no school for becoming a casting agent," she says, "and certainly not an ethnic casting agent. Basically, you need to knock on doors and say we're here, we want some representation, and we want to be in your films'."

Her clients are often students, paying their way through university by appearing in mobile phone adverts and comedies such as Chewin' The Fat, and in films like The Last King Of Scotland. For Andrea Arnold's award-winning, Glasgow-based film Red Road, the remit was to find 50 extras who looked like authentic asylum seekers. "I had to explain to the producers that half of them had only recently got their national insurance numbers and, to all intents and purposes, they actually were asylum seekers," she says.

Around half of the actors on Gyi's books are white European. Were she to rely on commissions for black and Asian actors alone, she wouldn't earn enough to survive. She is not a fan of racial quotas, and complains about a continuing sense of tokenism. If a white actor is better for a role than a coloured one, she would prefer to see them land the job. In short, she wants to see a mix, and at least part of her case is economic. "I know that only around 4% of people in Scotland are of an ethnic minority but if we want to sell these programmes across borders, there needs to be more ethnic diversity," she says. "You couldn't get away with showing a series like River City in Bristol because a lot of people there just wouldn't relate to it."

Getting her clients on screen, she says, is easier than dealing with the stereotyping that still exists. When an Asian is cast on a show, they are likely to be seen working in a corner shop; if the person is Chinese, they might be running a Chinese restaurant. It is an issue she thinks Scots should be able to sympathise with. "Whenever they want somebody hard in EastEnders or Holby City, it's always someone Scottish," she says, "and always someone from Glasgow. When images like those are reinforced, they get harder and harder to change."

There are reasons why Gyi deals mainly with extras. She says the dearth of prominent role models for ethnic minority actors in Scotland has created a vicious circle where people emerge, appear briefly in the public eye, and then vanish. She thinks she can count the exceptions to this rule on one hand: on her thumb and index fingers, Sanjeev and Hardeep Singh Kohli; on her middle finger, Shereen Nanjiani; on her wedding finger, Ae Fond Kiss star Atta Yaqub. Her pinkie wiggles free - she can't think of a single other. Without support, she says, the brain drain of genuine talent will continue to flow from Scotland to London and Manchester, as is the case with the ethnic majority.

Gyi argues that massive investment in the creative industries should be a priority for the Scottish Executive. It annoys her that True North - a film about illegal Chinese immigrants aboard a Fraserburgh fishing boat - was filmed in Ireland to keep costs down. She mentions the recent Ofcom report which suggested that spending by Scottish networks has fallen to just 3% of the UK share. When shows work, such as the multiracial children's programme Balamory, they are exported around the world; when the theme is universal, as in BBC Scotland's Still Game, Gyi sees it as a step in the right direction. "If something's good, it doesn't matter which races are represented, although there's nothing to say Ford Kiernan couldn't have been black," she says. "If the government could subsidise the film and broadcasting industry here for just 10 years, I think they would reap the benefits tenfold."

Should that happen, Gyi will be around to see it. Her home is Scotland now, thanks to the film that first attracted her. She has watched Local Hero dozens of times, and will watch it dozens more. Its landscapes of northeast Scotland still enchant her, as do the peculiar mix of characters. "Can you name the black actor who played the minister?" she asks. I can't. "Gyearbour Asante," she says. "Most people don't even remember him." She flicks through her folder again, before getting up to pay for her drink. "Things won't get better overnight but I'm trying to target people who are facilitators of change," she says. "I'm going to push - I'm going to just keep on making those calls."