Celia Imrie on age: "I'm not mad about it. I'm not mad about being the age I am. But I have to be honest. It's become a bit fashionable to be my age, bizarrely."

Now, at 64 years old, Celia Imrie has decided it's probably time she wooed America. And so later this year the star of Calendar Girls and The Best Exotic Marigold Hotel – and one of Victoria Wood's sidekicks in Acorn Antiques and Dinnerladies, of course – is off to Los Angeles to film a second series of the TV comedy Better Things, in which she plays Pamela Adlon's mum. And there's even a date on Broadway when the Old Vic's production of King Lear with Glenda Jackson in the title role transfers there.

In short, the most proper, well-spoken, well-mannered English rose is ready for her American close-up. If she can make it there, after all … "I don't think you can be internationally well known unless you do," she is telling me as we sit upstairs in a pizza place on the Portobello Road in London close to where she lives.

And she wants to be internationally well known? "Why not? I don't have much time left but if I go to America this year on television and on Broadway that might give people some ideas."

Time's winged chariot has, as yet, not caught up with her. Imrie is sitting in a corner of the busy room looking immaculate, hair just so, accent proper, manners impeccable (everything is "lovely". Even the waitress's lipstick: "How do you keep it on? Looks good").

Earlier this morning I had seen her in Gore Verbinski's big-screen, big-budget movie A Cure for Wellness, where she is playing older. She looks anything but, right now. Not that that is how she sees it. "Actually, I'm horrified when I see myself on screen now. That is rather a shock."

Truth is, I guess I'd always thought Imrie was from these parts. Blame it on the fact she can put on a good Scottish accent and first seeing her in Highlander, of all things. She did have a Glaswegian father and spent her formative acting years at the city's Citizens Theatre but, really, she is Home Counties through and through. She grew up in Guildford looked after by a nanny ("which in the olden days I would never have admitted to because it sounded too posh," she says) and wanting to be a ballerina.

When that fell through and after recovering from bouts of anorexia in her early teens, she turned to the stage. And over the last four decades and a half – her first IMDb entry is an uncredited appearance on The Fenn Street Gang (bonus points if you can remember which sitcom that was a spin-off from) – she has become something of an ever-present in British film and television. A kind of imprimatur of quality, whether it be in Dinnerladies, Gormenghast, Nanny McPhee (a real favourite of hers) or the aforementioned Calendar Girls in which she had to get her kit off (prompting Helen Mirren's infamous line: "Lawrence, we're going to need considerably bigger buns").

But, as noted earlier, for the last 10 years she's found that she's rather in fashion. "I'm very thrilled, bizarrely, to be the age I am because the parts I'm getting to play are insistent on being the age I am. Otherwise it wouldn't work in Calendar Girls or Exotic Marigold."

Her part in A Cure for Wellness is age-appropriate but slightly smaller than she would like. "My son reminded me of what Gore Verbinski said of my character, which I thought was brilliant because, of course, I'm a greedy pig and I want more. But he said: 'Ah yes, but she is the garlic in the soup,' which I thought was rather marvellous actually."

I'm not sure what flavour of soup the film might be. Possibly cabbage and candy apple or something. Set in an austere mountain spa retreat, it is, you have to say, a deeply, deeply silly film. But at the same time it's hugely entertaining and looks a dream. Verbinski has taken the script's gothic qualities and ran with them. Imrie is one of its minor pleasures but still a pleasure all the same.

In real life Imrie would probably be safe from its horrors because she would never end up in a spa in the first place.

"I'm not mad about them. I've done water treatment in a hotel. I didn't even like that very much. The idea of going to a health spa is like a mixture of hospital and prison. So, not up my street."

Has her career been the one she wanted, I wonder. "Not really," she says. "It's taken me a while to be taken seriously. Years ago I doubt they would have cast me in King Lear because people saw me more as a comedian, which, by the way, I love. But the only thing as an actress you can do is try to do something as possibly different as you can from the last thing, otherwise you're rather at the whim of whomever wants to employ you."

There's always the danger of the industry typecasting you then? "They will if you let them. Because they see you do something and they say: 'Well, let's get her because she does that, doesn't she?' And then you're stuck. I hate being stuck."

Why does she act? "Well, I have two nursing sisters who I think are angels. I do sometimes wonder what on earth I think I'm doing dressing up and pretending to be somebody else. But I also know every now and again somebody will say: 'Dinnerladies really cheered me up.' And I know one, TV can be a great companion, and two, there is nothing more than making people laugh."

Imrie was working in the United States last year when the news that Victoria Wood had died came out. Part of her still can't quite believe Wood has gone. "I didn't even know she was ill. That was ghastly.

"I say with great affection that I'm very, very proud to have been in her gang. However, she was quite a taskmaster. Anyone will tell you that. She wrote like music so she was very particular about every single word.

"But when I look back on it we had a great time. Because we were a team we knew each other very well and we came back together over a period of 20 years probably. That's quite a rare thing.

"I considered us to be great pals. I hope she knew how grateful I was. I always told her. She gave me a wonderful opportunity. It is the thing I'm most known for."

Celia Imrie on guilt: "You can plague yourself with it. I think it can be like chains around your ankles but I don't think you can necessarily stop it. Well, you can, you have to make yourself, but it will be there. I have a very loud conscience, Jiminy."

Say the word Scotland to Celia Imrie and she thinks Jimmy Shand and bluebells. "My dad was a very good Scottish dancer. He started the Scottish Society in Guildford, actually. Jimmy Shand was one of my Desert Island Discs. I'm proud of being half-Scots."

Her father was a radiologist. Her mother, Diana Elizabeth Blois Cator, came from a family full of earls and dukes and barons. Imrie was the fourth of five children. That might have some bearing on her desire for attention perhaps. "Oh definitely, definitely. My eldest sister was my father's favourite, my brother was my mother's favourite, the next sister up was my nanny's favourite and everybody loved my little sister because she was five years later."

"I had an extremely happy childhood but I suspect I spent a lot of time saying 'Hello!'" She waves for emphasis.

"In fact, I remember years and years ago on the radio hearing a programme about how if you were a boy and you threw a stone at a bird and killed it there is a chance that you might grow up to be a vet to make that horrible thing better in your life. And certainly my mother used to say: 'Go on, C, do your bit,' which I would hate in front of visitors. But am I trying to make that moment better?"

She considers the idea. "I think there is something quite deeply embedded in our make-up which makes us want to do it and we will never be satisfied. We will never stop wanting to do the next bit and the next bit and be better. I really do think it's quite a driving force."

It's too simplistic probably to suggest the anorexia she suffered at the age of 14 was linked to that need for attention. It's not something she is keen to talk about but what is striking, I suggest, is that by the age of 16 – just two years later – she was on stage acting, which if nothing else is a reminder of how flexible we can be as teenagers.

"I never thought of that. Actually, because I have to do everything in extremes, I had anorexia twice. I had it first of all when I was 11. The second time was 14.

"I don't want to go on about it too much, but I will always say you can kick it. I'm a very good example of someone who did manage to take themselves in hand and turn around.

"There was a nurse at Great Ormond Street who said to me: 'You do know you're taking up the bed of a really sick child, don't you?' That was the thing that got me."

So the fact that within two years she was doing pantomime is a sign of strength perhaps? "Actually, I love food so to starve yourself over 18 months, two years, that takes a perverse strength too."

The shadow of that time lingers, she admits. "For instance, I'm not going to eat anything in front of you. I'm still that silly."

There's a wilfulness to her, I suspect. She has never married, never wanted to it seems, and when she came to want a child she came to an arrangement with her friend the actor Benjamin Whitrow. His role was to be the biological father but the task of raising their son would be for her.

She has said in the past that "marriage traps you". For all her proper accent and upbringing there's a desire in her to be unconventional, it would seem. "Possibly. Yes, I think that is true."

Why so? "Umm, because I have a horror of being boring or ordinary."

She was already in her forties when her son Angus was born. She did leave it late, she admits. "You need quite a lot of energy with him which I think I did have. And his father is wonderful with him."

What has parenthood taught her? "Oh well, it's teaching me now to let go. Angus – deliberately Scottish because he looked like my dad when he was born – is 22 and in his last year at drama school and he's announced that he's leaving and that does fill me with horror. But I know I mustn't stand in his way. I remember my feeling of independence when I was 16 and got my first job. I always wanted to break away, so I must respect that."

Still, she says, it's good for an actor to have children. "I think my profession is quite selfish because you're always thinking about yourself and how you look and I think to have a child is a terribly good thing because it makes you think of someone else first."

Celia Imrie on desire: "To be desired is always something that any actress, if she's truthful, would want. You want to be adored by the audience. It's not just enough for one person to adore you. You want a whole audience full of people that night and then the next night."

Ambition, Celia Imrie says, used to be a dirty word, not to be spoken aloud. But now she is happy to admit that, yes, she is ambitious. Ambitious to be better. Ambitious to be better known. Ambitious to be break America. "I do think I'm running out of time and I do think health is terribly important and I don't like it if I get a bit stiff."

What would she like to do that she hasn't so far? "I think I would love to do a film where it was quite peculiar and I didn't have to look good all the time and it could be quite surprising to people."

A Cure for Wellness isn't that? "It's getting there, but I want more."

America, brace yourself.

A Cure for Wellness is screening as part of the Glasgow Film Festival on Thursday at 9pm at the Glasgow Film Theatre and goes on general release on Friday.