But don't just take my word for it, look at the polls. In market research, Walters shyly confesses, she consistently comes out at the top of the list of people the public would like to see advertising products on TV. Her appearances as Mrs Overall - a shambling old woman with a hairnet, a tea-tray and, of course, an overall in the spoof soap Acorn Antiques - on Victoria Wood: As Seen On TV were greeted with the sort of whooping that studio audiences usually reserve for members of Take That. (Walters enjoys playing old women: "I like the shape they get into. It fascinated me as a child. I remember looking at my grandmother and thinking, 'How did her nose ever get like that?' ") She won a Bafta, a Golden Globe and a Variety Club Award for the title role in the film of Educating Rita, Willy Russell's play about a working-class girl determined to improve herself through study - about which Walters still gets fan mail.
Alan Bleasdale, the writer of her latest television series, the epic, six-part Jake's Progress, chimes with public opinion. He has known Walters "since we were both babas" (ie when they worked together at the Liverpool Everyman in 1974) and risks accusations of luvvieness in his assessment: "Her ears'll burn forever, but I don't think you'll find anyone in our profession who doesn't hold her in the highest esteem. On Jake's Progress, we had a hard, Northern crew who can smell out a phoney at a hundred yards - especially if they're a thespian - but they all completely fell in love with her."
Munching her way through rice cakes, slouching in a sumptuous maroon armchair, unpretentiously dressed in a long denim skirt and black polo- neck jumper, Walters does not look very much like a star. Perhaps that's the secret of her success. She plays ordinary more extraordinarily than any other British actress. She is the girl next door, never out-of-reach glam, brought sparklingly to life on stage or screen. Think of the heightened pathos she gave to the downtrodden women she played in Educating Rita, the National Theatre production of Sam Shepard's Fool For Love, and Wide- Eyed and Legless, the BBC film about a woman suffering from ME. She is about to dazzle again in a down-to-earth role, playing Julie, a nurse and family breadwinner who has to cope with numerous crises - stroppy son, dreamy husband, bank repossessing her home, unexpected pregnancy in her forties - in Jake's Progress. The key to all Walters' performances lies in their psychological plausibility - the same quality that convinced the market-research interviewees.
Face to face, she is equally plausible. As she discusses her daughter's three-year battle with leukaemia (now apparently cured) or the shallowness of American TV interviews, and flashes her winning smile, you can't help but warm to her. Walters herself cheerfully confesses to adoring showing off; when I offer her some coffee, she hastily turns it down: "I'd talk you to death." In an hour and a half, I am in the presence of Barbara Walters, Baroness Thatcher, an American airline pilot, Walters' Irish mother, and numerous little girls and old women. Sometimes you feel like a dazed bystander at a Royal Command Performance. But mostly you just laugh. As Bleasdale puts it: "She really does light up the room."
Born in 1950, Walters was brought up in Smethwick in the Black Country (hence Mrs Overall's accent), where her father was a builder. She had wanted to be an actress for as long as she can remember. "It wasn't anything external," she muses, "just my desire to show off. We had curtains across the bay- window in our front-room. I'd get behind them with a ukulele and then whip them back - 'da da da' - and do a show. I was three or four." Expelled from school for non-attendance, Walters briefly went to nursing college to please her mother. Unable to resist the lure of the leotards, however, she packed it in and went to do drama at Manchester Poly, after which she joined the Liverpool Everyman in 1974. The Everyman's production of Ayckbourn's Funny Peculiar, in which she starred with Richard Beckinsale, transferred to the West End for 16 months, and she has never looked back.
Victoria Wood has been a friend for 17 years. They met in a revue at London's Bush Theatre called In At the Death: "It was very appropriately named," Walters recalls, "the audience were, every night." Wood and Walters hit it off at once and would console themselves about the revue by tucking into "liver, boil and chips" at the Bush cafe. Wood sums up her friend's acting: "She's a terribly observant person. Like a bionic woman, she picks up and remembers voices and attitudes. She's particularly good at doing emotion. I only like to go to the theatre to cry, and she made me cry in both Educating Rita and Fool For Love. She can also be warm. I love warm actors because they're the most life-enhancing. If theatre isn't life-enhancing, what's the point of it? To make your bottom sore?"
Walters admits to relishing pyrotechnical acting. "I love a bit of that. It's very cathartic. When my mother had just died, I had to do this play called Frankie and Johnny at the Clair de Lune. In it, there was this scene where Frankie has to talk about her mother who has died, and she has to cry. That was marvellous, heaving it up. It meant I could mourn her while I was working." She adds with a wicked laugh, "I was killing two birds with one stone, really." It all sounds terribly easy the way she puts it, but, of course, like a duck gliding across a pond, all the work is going on beneath the surface. "She's excellent technically," Wood reckons, "but she never shows you the wheels going round. She's also highly disciplined and puts a huge amount into it. She learns the words - that's a big plus for me. A lot of people turn up and busk it. I listen to them and think, I don't recognise that as a sentence I wrote."
Though jokey in person, Walters takes work seriously. She has a reputation in the business as the complete professional. Bleasdale reveals that "her way of working is like a boxer before he goes in the ring. For an hour before her scenes, she's very intense and goes into her own private world. She uses music a lot. She's got the headphones on - that's the only time you can't talk to her."
The Julie Walters Fan Club has not always been so vocal. Her career has taken some wrong turns: she herself describes Stepping Out, a dance extravaganza she did with Liza Minnelli, as "not the best of films"; while her performance in the dire 1985 comedy Car Trouble was described by Time Out as "unlovably vulgar". In the mid-Eighties, she was in danger of being typecast as a fluffy lightweight, or someone to call on for an undemanding "turn". Bleasdale concedes that "the feeling might have been that she was more of a comedian than an actress". As if reacting against this, Walters took on Lady Macbeth opposite Bernard Hill at Leicester in 1985. Despite jibes from the press ("Journalists rang up to ask if I was going to do it as Mrs Overall") she made a good fist of it, and little criticism of her as a straight actress has been heard since. In fact, in Wood's view, "she is very good at proper, la-la-la acting. She can do things like American accents and wearing wigs."
This month, Walters starts work on Intimate Relations, a murder-mystery with Rupert Graves for cinema release next year. She is now in the happy position of being able to turn down 90 per cent of the roles she's offered: "It's mainly quirky, mad people in sitcoms that aren't very funny," she says. Bleasdale reckons that "she'll work forever. Sometimes the best of actors become typecast. She hasn't. For some actors - especially, unfortunately, women - the parts start to dry up when they reach 40, but her career will be as long as she wants it to be. She's got such range. In GBH she played Robert Lindsay's 76-year-old mother. In Jake's Progress she is playing his wife - we won't go into the subject of Oedipus now. Look, she can even make a Clorets' ad funny. That is talent."
! 'Jake's Progress' starts at 9pm on Channel 4 this Thursday.