How love, actually, has kept Bill Nighy and his partner together

Diana Quick is about to turn the tables on her partner, Bill Nighy, whose career has recently soared into the stratosphere with outrageous performances in the films Love Actually and Pirates Of The Caribbean.

While Bill has been strutting his stuff as washed-up rock star Billy Mack and evil pirate Davy Jones, Diana has been content to star in critically-acclaimed but fairly low key productions in the theatre.

But now she is returning to our TV screens - for her first series since playing Sebastian Flyte's sister in the television classic Brideshead Revisited 25 years ago.

Diana's new role in the BBC2 sitcom Sensitive Skin is as a sexy 60-something woman who has a 30-something toyboy lover. 'I'm having great fun playing a role like this. Even these days it does seem to be more unusual for an older woman to have a much younger partner than the other way round.

'And yet I have known several women in that situation. I remember meeting three women friends in a theatre bar one night and they were talking about their boyfriends who were all half their ages. I don't think any of the relationships have survived.

'I have lots of male friends who are much younger than me but I have never met anybody younger where I've felt we could be kindred spirits. I have never even had an affair with somebody younger than me. I think the sex would be complicated. I would feel quite weird, sexually, with a younger man.'

Her own relationship with Nighy has lasted 22 years, despite its unconventionality. They have never married, preferring to refer to each other as the 'POSSLQ' ('person of opposite sex sharing living quarters') and seem to spend almost as much time apart as they do together. For example, when Diana turns 60 later this month, Nighy will be starring in the David Hare play, The Vertical Hour, on Broadway.

They are presumably faithful, although Diana has said in the past: 'Physical passion was important to me when I was younger, but I find I don't really need it in my life anymore. Once in a while the chance to have an affair comes my way, but it doesn't tempt me.'

Perhaps regretting her openness in the past, she now resolutely refuses to discuss their relationship, which has somehow survived Nighy's years of alcoholism and drug addiction which he finally beat in 1992.

'We have this policy of not talking about each other. I'm very proud of him but I just don't want to discuss our life together.'

The couple met in 1984 when they were starring in a play at the National Theatre. Diana had previously been married briefly to the actor Kenneth Cranham and had a relationship with Albert Finney which lasted for seven years, despite his infidelities.

She was feted as one of the most beautiful and talented actresses of her generation and, around the time she met Nighy, a Sunday-magazine ran a cover of her with the caption 'Is this the most beautiful women in the world?'

'I don't think I was,' she demurs 'And I've never seen the magazine.'

But on the cusp of 60, she is still a remarkably attractive woman. 'I can't quite believe I'm going to be 60 and collecting my buspass and getting my pension.

'It feels very strange. When I was growing up, the expectations for a middle-class girl like me was that you would work for a while, then get married, have a family, and that would be your world. But it's so different now.'

Diana grew up in Kent, the third of a dentist's four children. But she herself left it until late in her career to have a child - her and Nighy's daughter Mary, who is now 22.

Diana says: 'When I was younger, I thought I had all the time in the world to have children and all I really wanted to do was work. But I had quite a lot of pressure put on me by our family doctor who was also a friend.

'When I went to him for advice about birth control he would continually ask when I was going to start having babies. I would say I didn't want them now and wasn't it better to have them when I wanted to and wouldn't resent them.

'He said it was better, physically, to have them when you are young and I think he was, up to a point, correct. I was physically well when I had Mary at 37 but I didn't have any more children. It would have been nice for her to have had a brother or sister but it just didn't happen, so perhaps I should have started a family younger.'

When Mary was two-and-half, Diana was behind the wheel of a car when they were involved in a car crash and the child had to undergo six hours of surgery.

'Because I was driving, I felt absolutely wretched. I re-ran it in my mind, wondering if there was anything I could have done differently to save us, but it was a monster pile-up in fog and we went straight into the tail-gate of a lorry.

'Mary suffered serious internal injuries because of the impact against the seatbelt. All my energy went into willing her to survive and, thankfully, she has.'

Although she is not given to effusiveness, Diana clearly dotes on her only child and is rightly proud of the rapid success Mary has had in her fledgling film career.

She appears with Kirsten Dunst in Sofia Coppola's sumptuous film Marie Antoinette and was recently chosen as one of ten female ' Breakthrough Brits' by the UK Film Council, which flew her out to Hollywood to meet and greet 200 movie executives.

'I sound like my mother when I say one doesn't really want to see one's child go into showbusiness and face yawning gaps of unemployment, but she seems to have done well so far.' Having waited so long to have a child, Diana admits that she made sacrifices in her own career for the sake of her daughter. 'I felt very strongly that, because childhood is so short, I wouldn't be away from Mary for more than two weeks at a time. So I said "No" to a lot of jobs.

'I did that for about 19 years because I think one has to make choices - and I chose parenthood. But now that she has her own life, it has completely freed me and I can look at each job on its merit.'

Such a job was the eponymous lead in Brecht's classic anti-war play, Mother Courage And Her Children - a part previously played by Judi Dench, Diana Rigg and, most recently, by Meryl Streep on Broadway.

The play is on tour in Britain with the hope that it may come into London's West End. Set during the Thirty Years War in the 17th century, its is about a woman, played by Diana, who travels the battlefields of Europe with her three children, risking all their lives to sell supplies to the soldiers.

'The play is still so interesting and relevant today in that war goes on all the time and is waged by governments and economic powers, not by women and children who are usually the main victims of it.'

An intelligent and articulate woman - she got a scholarship to Oxford University before she had even sat her A-levels - Diana has many passions apart from theatre, and writing is one of them.

She has spent the past seven years researching a book about her paternal family's life in India which she hopes to publish next year.

Her great-grandfather served 23 years in the Army in India before becoming a policeman and her great-grandmother had to flee from the Indian Mutiny after her father was killed.

As part of her research, Diana and her daughter spent last Christmas and New Year retracing her great-grandmother's flight across what used to be known as the Central Provinces. 'We found all the places she had hidden in from marauding mutineers who would have killed her. We had a fantastic time.'

An adventure that makes Bill Nighy's exploits in The Pirates Of The Caribbean sound like play acting.