GEORGIE Glen's acting showreel reveals real talent.

Short 20-second internet clips from the likes of Waterloo Road, Heartbeat and Calendar Girls convey a vast range of nuanced, very different, some surprising personalities being played out; there's none of your John Wayne/Sean Connery playing-yourself stuff here.

Yet, when you meet the Helensburgh-born lady in person, there's an even bigger surprise in store. Glen's confidence seems to run in inverse proportion to her talent. While she's able to leap across the character chasm from deferential maid (Mrs Brown) to confident cop (Heartbeat) effortlessly, the actor admits she could never imagine herself as Lady Macbeth or Ophelia.

The 58-year-old may be at an age when her Norma Desmond or Blanche Dubois would be wondrous to behold, but Glen reveals she won't be going anywhere near these fantastic, fragile females any time soon.

"I've never enjoyed playing leading parts," she says over coffee in Film City, the building that formerly housed Govan Town Hall, in a warm voice and accent that's travelled far from her home town. "I just don't have the confidence to play a leading role. I think I have a place in the profession and that place is in a supporting role. But I like supporting and I think I'm good at that."

Saying most actors crave leading roles is like saying Meryl Streep does accents. They live to stand in the spotlight until their eyes sting and their ears ache from the sound of applause. But not Georgie Glen.

"If you play Lady Macbeth you are setting yourself up to be knocked down," she argues. "Maybe I'm in a safer place, playing a cameo where you can come on and shine." She thinks for a moment. "John Hurt once said 'Good acting is about catching the ball, running with it and then passing.' And I like to get rid of the ball quite quickly. I'm not a try taker."

This isn't a case of Glen being bitter about not getting the top roles. "I was offered an Ayckbourn lead in A Woman In Mind. But I watched Julia Mackenzie do it in the West End and I thought I couldn't do it justice. I feel the weight of responsibility far too much."

Glen's unusual approach to the business of acting is perhaps explained by her unusual entry route. "I never appeared in plays at school," she recalls. "I was always the helper with the set. The thought of acting didn't enter my head. My dad [the MD of Westclox] once played piano and saxophone, and there was fun at home after dinner - it all sounds rather Victorian - but I never felt to take this further."

Glen studied graphic design at Glasgow School of Art and in her mid-twenties moved to London to work for a book publisher, designing covers. "I felt isolated because the evening diary was empty," she says. "So I found a mag listing local authority evening classes. Then, perhaps unconsciously, I chose performance related subjects, like Tap Dancing For Beginners, or Solo Singing For Beginners."

Enthralled, she then auditioned for Questors Theatre Company in Ealing, watched the semi-professionals at work and learned, gradually taking on small roles. "I loved the world, but I wasn't desperate to be up there on stage. The first part I had was in The Philanthropist and I didn't have a line to say. And it was perfect."

Glen attended Questors every night. Always mad keen. Always early. And she gradually found her voice. One night, Alan Rickman (who had also been a graphic designer and gone into acting in his late twenties) watched her perform. "Sometimes I think the universe takes control of our lives," says the actress, smiling. "And this was one example. Alan said to me 'Write off to drama school. Tomorrow.' And I did. Literally."

She was accepted by Bristol, where her contemporaries included Mark Strong and Jeremy Northam. "If I hadn't been accepted I'd have walked away from professional acting."

On the last day of drama school, Glen was offered a job at the Wolsley Theatre in Ipswich. Rep theatre taught her to do "anything and everything". "It was incredible," she says of the experience. "I'm sad young actors don't get the chance to do the range."

Aged 30, however, Glen knew she would never play Juliet. "Yes, but having a face like a squashed cabbage meant I would never play these sort of roles anyway. However I was the right age for 'character parts'." Shouldn't all acting be character parts? "Yes. Absolutely. But I think we know what that means. It's playing the Nurse rather than Juliet. It's being the Maid rather than the Queen."

Glen was a handmaiden to Dame Judi's Victoria in Mrs Brown. She would have played the Queen - but only if the Queen was a supporting player in the drama. "Don't get me wrong, it's not great when you are in a TV show or a play and the donuts come round and you are bypassed because your part is so small and you haven't even shaken hands with the director. I like to be respected as a supporting actor. But then again, I believe there's no such thing as a small part. Look at Breaking Bad [the hit US TV drama], every single part is great. And yes, I would have taken the role of Skylar."

Glen cites great acting sidekicks such as Annette Crosbie and Bridget McConnell. And she loved working with Dame Judy and Helen Mirren. "When I was asked by the director of Calendar Girls if I'd be prepared to take my clothes off, I said 'Yes, of course!', never having done it before. But Helen gave me a great tip for the day of nudity: 'Wear a pair of high heels, Georgie! It'll make you feel powerful.' And it worked, me standing there next to my shrub wearing nothing but gardening gloves, heels and a grin."

Are there enough roles for older women these days, 'character' or otherwise? "Mmm. As you get older there are definitely fewer roles. When something like [fantasy drama] Outlander comes along, you get excited until you realise there are 998 men and two women. Yet, there are a few things out now where women are getting good parts to play, such as Vera and The Honorable Woman." And Boomers, the BBC One comedy featuring mature performers? "Yes, I'm in episode three."

Of course she is. In a supporting role. And Glen doesn't regret not being part of TV's A-team pool, almost always led by the Steadmans and Redmans. Perhaps it's because she always makes a mark. Her Waterloo Road teacher Audrey McFall, for example, is multi-layered and recently found herself a toy boy. Is the older woman/younger man pairing something Glen (a mother of twin girls and wife of actor Richard Braine) supports?

"I've never quite understood these cougar women," she says, grinning. "The women do it because they can. They can remain more sexually alluring to an older age these days, and it's empowering. But I don't think it's a happy way to go. I think it will end in tears. You can't hold the tide back."

Glen seems to have few professional worries. She's perfectly happy knowing work keeps on coming, whether in straight drama or comedy, in films such as Shakespeare In Love and My Week With Marilyn, or on TV with the likes of chum Harry Enfield. Glen has recently filmed an episode of comedy series Bob Servant, plus "a couple of pilots with Alan Davis and Jo Brand", and a huge Disney TV project called Evermoor. "Yes, the work comes along, but even now I'm shy about performing," she says. "I can't believe I'm doing this. The world is full of wonderful actors, and I still feel a fraud."

Disappointments? She would have liked Waterloo Road to run on, but it has been announced that the school drama will end next year. Did she feel lifting the leviathan production up north to Greenock proved to be the undoing? "I don't know. Maybe it had its natural life after ten years. But I'd love to do a spin-off with Audrey and Maggie [played by Melanie Hill]."

After a couple of hours with the actress, you realise she really is a rarity, a creature who loves to slip under the radar and then explode. And why not? Perhaps it's the Scarlett Johanssons of this world who are missing out on the great character parts?

"Well, she doesn't get to play the old biddy in a bonnet, does she?" says Glen, grinning. "But I'm not sure Scarlett is too worried about this."

Glen's old biddies are great, as it happens. But you can't help thinking it would be great to see her in the donut roles.

The next series of Waterloo Road begins on BBC One on Wednesday at 8pm