A couple of days after meeting Jenny Agutter at the National, where she is busy rehearsing Peter Pan, I come home to find a message on my answerphone. "Hi, it's Jenny. You remember we were talking about what journey Mrs Darling makes during the play? Umm. I've been thinking about it some more. The journey is that she grows up. Does this help at all?"
Well, yes, it does thanks very much. In fact it rounds things off rather nicely. Because for Mrs Darling we could easily be talking Jenny Agutter. You see, mention Ms Agutter and most people automatically think The Railway Children. Never mind that the film is the best part of 30 years old, and that Agutter has performed countless roles since then. Somehow she has become preserved in a time-warp as the sweet and innocent Roberta.
And I'm as guilty as anyone of doing this. When I first heard that she was appearing in Peter Pan, I automatically assumed she must be playing Wendy. And even once I'd got my head round her playing Wendy's mum, I was still momentarily taken aback when a stylish woman in her mid-forties breezed into the interview room, rather than some post-adolescent ingenue.
Unlike some actors who get annoyed when you go on about past glories ("We're here to talk about what's happening now, godammit"), Agutter seems completely at home talking about The Railway Children. Indeed she is quick to acknowledge its importance in her career.
"The film captured a mood," she reflects, "and it certainly got me noticed. I doubt very much whether Peter Hall would have invited me to the National when I was just 20 to play Miranda opposite John Gielgud without it."
And that's not all. The Railway Children also secured her a part in The Snow Goose, for which she won an Emmy, and when she decided to leave this country for LA she walked straight into a role in Logan's Run and a contract with MGM.
In many ways, it all sounds pretty much ideal, and Agutter isn't in the business of bursting too many bubbles.
"Children are often thrown into things emotionally far too quickly these days, before they have had a chance to play them out," she says. "I was lucky. As an actress I got to play as much as I liked. People always treated me as if I was young. My publicist insisted that any interviews must first and foremost be fun. So he always made sure there were loads of cakes and ice-creams around."
Since we're both piling into a massive plate of sandwiches, it occurs to me that maybe she still has the same publicist, but for once I don't allow myself to be side-tracked because I'm having trouble believing it was all that idyllic. And when pressed she does admit there were drawbacks. "I was extremely precocious in my behaviour, without being particularly grown-up," she says. "If being adult is knowing who you are then that was put off well into my thirties."
But she is grown-up now. She's moved back to this country, she's happily married to a hotelier and has a young son, Jonathan, whom she obviously adores. So why is everyone still so keen to pigeonhole her as Roberta? And how come we can all overlook her many nude scenes - Walkabout, Equus and An American Werewolf in London come instantly to mind - and still think of her as that nice Jenny Agutter? I mean, some actresses only have to flash their boobs once to get branded as some kind of screen tart.
Well, for one thing, Agutter is unquestionably nice. Most people can scarcely remember what they've said during an interview, let alone be bothered to think about it and leave a message a few days later. And she has an openness and a vulnerability that instantly makes one warm to her.
Few actors like to admit they have taken parts that others have turned down, but Agutter can turn self-deprecation into an art-form and launches into a long and very funny story about how she came to wind up both in When the Beat Goes On, courtesy of Jane Asher, and on tour in Japan with Love's Labours Lost, courtesy of God knows who.
It's almost as if Agutter has become an icon for lost innocence, a symbol of happier, gentler times, within our psyche. But if this has always guaranteed her work, it hasn't necessarily done her any long-term favours, because her career has never really reached the heights one might have expected after her glittering arrival on the scene.
For with her vulnerability came an almost painful lack of self-confidence. Rather than build on her Miranda at the National she dashed abroad to do films, because she had found the whole experience too traumatic. "Peter Hall told me to stick with the classics," she says, "but I just didn't feel strong enough. I didn't think I had the technical skills."
And although her CV isn't littered with turkeys, many of the films and TV programmes she has appeared in have been distinctly average. Rather than wait for the right role to come along, Agutter was always willing to accept once that would do. It is almost as if she feared she might be forgotten if she wasn't working, and that acting was the only thing that made her feel alive and valued.
"I never felt comfortable selling myself as an actress," she confides. In Hollywood everything's always got to be wonderful and terrific and your career is always goin' places. Even if you're not working, everything must still look perfect. I could never manage that. If someone asked me what I was doing when I wasn't working I would say, "Nothing". And people would look at me as if I was infectious. So in the end, I guess I just didn't believe in myself enough as an actress to risk not working."
But things changed a little in her mid-thirties. The flood of young female lead parts slowed to a trickle, and her sweet-natured public persona began to develop one or two cracks. "I always thought I'd have more emotional control as I grew older, but I've found I have less and less," she says. So these days we get to see much more of the angry, neurotic side of Jenny Agutter.
She confesses to having had every available test going while she was pregnant with Jonathan, and to growling and sniping at anyone who gets in her way when she's throwing a moody. And as for relaxing, forget it. "I like to think I can slob around and do nothing," she says. "But when it gets down to it, I can always think of a number of chores that need to be done before sitting down. I'm a great organiser - but don't confuse that with being efficient."
Ironically, though, the less emotional control she has, the more control she appears to have over her career. She is now far pickier about what roles she accepts, is happy to take time out to be with her family, and has the self-belief to return to the National after a gap of 24 years to appear in Peter Pan.
Yet, for all her maturity there is still something engagingly young about Agutter. So where does that leave her on the developmental continuum? A fair grown-up child? I think both she and Mrs Darling might just settle for that.
`Peter Pan' is at the Olivier, National Theatre, London SE1. Booking: 0171-928 2252