We're half in, half out of reality here. The room is just an ordinary office with some cupboards and two squishy sofas, but if I lean forward and look out the window I can see a bus headed for a destination that doesn't exist. Then there's the time difference: inside, the heating is on because it's a cold day in April, but outside it's already June, it's hot and everyone's walking around in summer clothes. In here it's just a room in an office block; out there it's soap-opera world.

Louise Jameson, who is sitting opposite me on the other squishy sofa, is half in reality, half out of it, too. The bottom bit is hers: a beautiful knee-length coat smeared in gold leaf, but the hair and make-up belong to Viv Roberts. Viv is the hairdresser who has just moved into Shieldinch, the pretend part of Glasgow where the soap in question, River City, is set. For an hour or two, Louise has stepped out of Viv to talk to me about the part and lots of other stuff, too, such as facelifts and riots and being a single mum and trying to be liked, and some of the roles she's played.

For some reason, most of those roles have been in big one-word hits: Bergerac, Tenko, EastEnders, DoctorWho. Together, they've made her one of the most recognisable faces on the telly for a good 30 years, so whoever it was at River City that thought of her for Viv knew what they were doing. "Viv is a single parent with two kids by different dads, best friend's gay, drinks a bit too much," says Louise. "I thought Oh my God, has someone been a fly on my wall?'" She throws her head back and laughs.

But we can get on to all of that later. First, it makes sense to talk about something else; something summed up by a phrase that's pretty much always lurking in front of Louise's name. There it is, just in front of the L: "former Doctor Who companion". Most of the actresses who play the Doctor's assistant suffer from this label, maybe Louise more than others because her character was so memorable. She played an alien savage called Leela, bright but uneducated, with an uncompromising avenging morality. She was brilliant in the role, feral and frightening, and boys in the late 1970s couldn't believe their luck when they saw the leotard she was almost wearing at five in the afternoon. It was a great part and - long before Billie Piper - arguably the first Doctor Who assistant to break the stereotype. "I would love to come back as Leela on camera with a football team of grandchildren," says Louise, 30 years on.

She clearly loved the role ("it's been my lifeline to the business"), even though playing it wasn't entirely happy for her at the time. She and the Doctor, Tom Baker, had a volatile relationship, she says.

"We get on very, very well now but at the time I didn't stand up to him like I would now. He didn't want to travel with a companion and that overlapped into me feeling that he didn't like me. Instead of sitting down and discussing it I just went to weep in the corner." Eventually, about half way through her run, on the set of a story called Horror of Fang Rock (the one with the lighthouse), she negotiated a truce. "I did have a little word with him about a particular scene and I just said, Let's think about the programme,' and then after that we seemed to get on much better."

Maybe it's not a surprise that Louise and Tom struggled to get on. They are certainly very different people. Yes, Tom is brilliant and funny, but talking to him is a bit like shouting up at a very big cliff. Louise is different: talking to her is like sitting round a two-bar electric fire. She's very warm and easygoing, with eyes that pay attention to you. I should talk about those eyes ,actually. They are blue blue, and so striking they were even written in as a plot in that episode of Doctor Who I mentioned.

All of this gets us round to talking about how Louise looked back then, and that leads to something else interesting: how she deals with her looks changing over the years. While she was going through the menopause, she says, her self-esteem was low, and she decided to try a solution many people her age (she's 56) turn to: the blade of the plastic surgeon. "I thought, OK, well how do I get the self-esteem back? I know, make yourself look like you used to.'"

She went to the surgery and the doctor used some clever software to show her how she would look after the operation, and she booked an appointment for a facelift. And then she got a job that cut across the date. "I said I would call them when I was free and I never called," she says. "I suddenly was feeling better about myself; I'd somehow come through that stuff."

Now, when she talks about how close she came to having that facelift, she seems slightly horrified by what she nearly did.

"The first lift lasts five years, the second one lasts two and a half, the third one lasts six months - and then there's no skin left to stretch. You're buying seven and a half years of youth and then you're just going to look weird." She pulls back her cheeks with her hands to demonstrate and thinks about what she nearly did.

She's clearly pleased with the decision she made - and it was a brave one, I say. No, she says, not brave. In fact, she's not brave at all. All those brave and bolshy characters she's played - Blanche in Tenko, Leela in Doctor Who, Viv in River City - are in a way what she would like to be. Dare to be.

"What I feel is inside me," she says. In fact, she insists, she has always been a good girl. She went to an all-girls private school, but never bunked off or swore. Through her teens and twenties, acting took up all her time. And then, suddenly, things changed when she turned 30. "I got pregnant," she says. "When you have two kids out of wedlock, you stop being a good girl, don't you? It was difficult for my parents to take. I got pregnant with Harry, who is mixed-race, at the time of the Brixton riots. It was a slightly rocky time in London."

Later, she had another son by a different father and struggled to bring both of them up on her own. "I couldn't be both parents. I couldn't be the breadwinner and the hands-on mum. I couldn't do either job properly." Then it got even worse as the boys stomped into their teens. "My sons were 'orrible teenagers and I was more or less on my own. I had sleepless nights and tears." They've come through the other side, though, and things are great. Tom is 23 now, Harry 25, and they're both personal trainers. She says her experience with her sons makes her worry about today's youth, about the fact there isn't enough for them to do except get drunk.

It doesn't surprise me that Louise worries like this; there's clearly a strong caring streak in her. She famously chummed Leslie Grantham though prison and now she's got up and done something about the teenagers by starting a Sunday drama college for them. Imagine! Louise Jameson as your teacher! I bet some of the boys go slightly red when they speak to her.

The college isn't the only interesting project bubbling away for Louise: she is part of a writers' group with 13 other writer/performers. They've been working on ideas and have now come up with such a good one that they're going to pitch it to producers. I ask her what it is, but she presses her glossed lips together and mimes a zip. Then there's Louise's stand-up, which she's been developing for a little while. She's even done a couple of gigs, with the theme Love Me, Love Me, Love Me. Now, she says, she just needs to toughen it up a bit. "What's brilliant about the best stand-ups is that lack of censorship between the brain and the mouth. I need to get to the point where I don't care." Why stand-up, though? "I must need attention, mustn't I?"

She's sometimes had too much of that. Has she ever had a stalker? She pauses and then slowly says: "yeah". "I dealt with it in a low-key way, though," she says. "I just got a friendly policeman to go and have a friendly word. I didn't want to use a heavy hand. I just . . ." she waves her hand gently in the air ". . . sorted it."

It's typical, really, that even a stalker should get a gentle brush-off like this. Louise Jameson may often play in-your-face women, but she's an in-your-arms kind of person: warm, accepting. Some people forced to commute to southern England from Glasgow twice a week might let it get to them, but she shrugs her shoulders and says it's fine. If her contract with River City is renewed, she'll buy a flat in the west end - nothing big - and slip down to her favourite bar, Oran Mor, for a coffee. Leela sipping a latte in Oran Mor. I like that.

  • River City is on BBC1 Scotland tonight at 8pm; Doctor Who is on BBC1 on Saturday at 6.20pm. Louise Jameson will be appearing at the Army of Guests convention at the Quality Hotel, Glasgow, on Sunday, May 25. For more information, visit www.glasgow-who.co.uk