Unicef saved Audrey Hepburn's life as a child in Holland at the end of the war just as it was going to save the Sudanese boy's life, and that is one reason why she is so proud to be a Unicef ambassador. It is the repaying of a very personal debt. But there is a deeper connection with the war years, one which brings her to London this week, not only to raise money for Unicef through public performance, but to pay tribute to the unquenchable spirit of the child in trouble through the life of one individual, Anne Frank.

On Thursday, at the Barbican, Audrey Hepburn and Michael Tilson Thomas conducting the London Symphony Orchestra will be presenting their version of the life of Anne Frank through the words of her diary and Tilson Thomas's specially composed music. It is a project which has returned both Tilson Thomas and Audrey Hepburn to their own youth through their identification with the undisguised turbulence of Anne Frank's own adolescence, one in which every emotion was intensified by incarceration and fear of capture. This is powerful material enough, but for Hepburn the connection with Anne Frank is even more personal.

When I met her to talk about it she was perched in a plush Claridges suite. I was expecting sophistication, elegance and a polished film-star performance. I had been told that she was every good thing from hard-working, generous and thoughtful to charming and downright divine. This undersold her, making her sound bland. The woman I met surprised me by being passionate, unpretentious and extremely down-to-earth. It took only a few minutes to realise that with Audrey Hepburn, what you see is what you get.

The first thing you get is the familiar face, one which, I suspect, doesn't spend too long gazing at itself in angled mirrors, other than in the line of professional duty. She wears very little make-up. Her hair is pulled back into a basic stretch-towelling pony-tail band. Her only jewellery is two small rings. She is wearing a white sweater and navy slacks and, when she leaves for the airport, she picks up one swiftly packed overnight bag. This lady is fastidious but not vain. At 62, she is also matter-of-fact about and comfortable with ageing, as well she might be. Her immediately recognisable beauty comes from a truly wonderful smile and a nice arrangement of slender bones which give her the kind of fashion-drawing outline other women sigh for. I suspect she will become very impatient if she reads this guff and wonder when I am going to get to some serious point, but it is a fact that when I tell people I'm going to see Audrey Hepburn, 90 per cent of them automatically say "elfin" and the other 10 per cent say "gamine". So, unfortunately, looks count.

When I raise the subject of beauty she sighs and says: "I still don't see it." What I suspect she sees - as most of us do in our own looks - is her adolescent self, scrawny, gawky, sick and undernourished, but still full of life and vigour, hanging over her window-sill to watch the passers-by, entranced with the imagined drama of their lives. Like Anne Frank, who was in hiding in Holland at the same time, she experienced the terror of the Nazi occupation and her own family tragedies - her father walked out for good when she was six - along with a child's natural irrepressible excitement about life which, in Anne Frank's case found an outlet in her diary, and in Audrey Hepburn's case, was the wellspring of the emotional energy she drew on in her film career.