Stardom has taken 65-year-old Phyllida Law by surprise. When she escorted her elder daughter, Emma Thompson, to the Oscars, Law came on like a teenage groupie. "That sort of thing doesn't happen in normal life in NW6. It was a Disney, Technicolor bubble. You think, `I didn't do that, did I?' It was like a waking dream. Placido Domingo stood on my train, and I had to ask him to move.
"I've even touched Al Pacino," she almost gasps at the memory, before explaining, "Many women say that you become invisible at the menopause. But I've just got louder. It's very good being elderly in a way. You're beyond the pale and can get away with things."
This late-in-life fame was thrust on her by her then son-in-law, Kenneth Branagh, who cast her in the key role of trusty housekeeper to Peter (Stephen Fry) in Peter's Friends.
"I owe young Kenneth Branagh a very great deal for Peter's Friends, I shall never forget that," she says. "It was a very well-written part, and it had scarcity value because I was the only elderly person in it, so people remember it. Sam Goldwyn is reputed to have asked Ken, `Where did you find her?' He replied: `She's my mother-in-law.'"
Fewer and fewer people will be asking who Law is after her latest performance, as a difficult elderly woman trying to patch up her relationship with her recently widowed daughter (played by Thompson) in Alan Rickman's beautifully acted directorial debut, The Winter Guest. The film offers the frisson of a real-life mother and daughter in the roles of their fictional counterparts.
The casting obviated the need for background work. "Although Phyllida and Emma are not these characters," Rickman reflects, "their physical ease together and generosity to each other and all of the other actors speaks volumes on screen."
Law underlines that their actual bond gave them a shortcut to the imaginary one. "For a start, we don't have to work at what we look like," she observes. "We must have the same body language, voice and tone. We cut a lot of red tape. A lot of the relationship is unsaid - which is a very important ingredient. It's a colleague you know bloody well. You know they bleed and make you laugh."
Law makes for invigorating company. Sipping a glass of wine in an upstairs London bar, she has the bone structure, voluminous hair and dress sense to walk away with any Glamorous Granny title. More than that, she has an infectious, almost flirtatious twinkle; you don't have to look far to see where her daughter got her sparkle - or her cheekbones - from.
Left a widow some years ago by the death of her husband, Eric Thompson, the creator of The Magic Roundabout, Law is, like all mothers, inordinately proud of her daughter's achievements. For all their closeness, however, mightn't the intense portrayal of a bickering mother and daughter have seeped into off-screen friction? Law is horrified by the very idea. "How could a mother and daughter be competitive?" she asks. "That would be obscene. There was not remotely any rivalry. If anything, Emma's too tenderly careful.
"If our relationship in real life had been similar to that, it would have been difficult and embarrassing," Law continues. "Because it's very different, it was easier to play. Acting with your own daughter did pack an emotional intensity, but we got rid of all that in rehearsal. If I'd been allowed to spill out private grief on screen, Alan would have been terribly severe."
Law herself becomes severe on the subject of the intrusiveness of the tabloids, who seem to think that Emma Thompson blowing her nose constitutes a good story. "I've found it unspeakable," Law says, angrily. "I don't take a newspaper anymore. If I read about something I know about, and it's inaccurate - which is a polite way of putting it - then how am I to believe the rest?" It's the absurd punts the papers take that most get up Law's nose. "Emma is supposed to have had affairs with every person in the world - it's just ridiculous. She's very sanguine about it. She says the press are like ratty parents; if you're getting above yourself, they come and biff you about the lugholes. Whatever image comes across, it's got nothing to do with her. If you can put the image aside, then it's easier to deal with.
"The tabloids even followed us to Scotland, where we filmed The Winter Guest. They had tape-recorders in their handbags and were offering money to the drivers. One journalist rang Emma and said, `I hear you're having an affair with Sean.' He was a little boy of 13."
A woman who could take self-deprecation as a chosen subject on Mastermind, Law cannot see her moving performance in The Winter Guest leading to other work.
"I can't ever imagine anyone is going to employ me," she sighs. "A nice film about a witch would suit me. I have to pin my hair up in the morning, or else it frightens the postman.
"I haven't had a blazing career; I just act when I'm asked. I've never been young-looking or beautiful. It must be hard for someone who's made a career out of being sexy and glamorous. It's not a problem I've ever had. I was playing old ladies when I was 19. I'm not going to start playing romantic leads now. Robert Redford is still acting in love scenes with women half his age, but it doesn't happen the other way round."
As I make my way out of the bar, she calls down the stairs with a faux serious face: "Do you think I'll work again? I could always go and make dolce puddings.
`The Winter Guest' opens today.