BRIAN Cox and his wife, the German actress Nicole Ansari, are a chiaroscuro couple, a study in contrasts. She is dark and glam, all leather trousers and decolletage; he is white-haired and crag-faced, Mount Rushmore in the snow. We are in their local North London gastropub, and they are trying not to gush when they talk about living and working together. Earlier they watched a recording of the recent ceremony to renew their wedding vows and are feeling quite moved as a result. They are keen, though, that this interview isn't a nauseating festival of mutual appreciation. Of their marriage, Cox says, "It's not all a bed of roses, " then laughs. "Well it is a bed of roses because it's got prickly bits as well."

On the face of it they are an odd pairing.

She is 36, raised in Cologne, the daughter of a German mother and Iranian father. He is 60, survivor of a tough Dundee childhood.

However, the age difference does not appear significant. She is an old soul, wise and at ease, while he has more energy than ever. Having young sons - Orson, who is four-and-a-half, and Torin, not quite two - has been good for them.

They met in Hamburg in 1990 when Cox was playing the lead in King Lear. Ansari went to see Lear eight times during its run.

"I met Brian at a party and there was just an instant connection - It was like meeting a soulmate. He understood me. We were just talking, talking, talking."

In 1998 they became a couple and a year later she moved to London to be with him.

"Brian's career was soaring at that time, but my career when I came here stopped, cold turkey, " she recalls. "In England it's difficult as a foreign actress. They don't even give you a chance. That was very hard for me because I had been working since I was 12 years old. I had to make a decision whether I wanted to live like that - as the wife of a famous actor, the wifey basically."

She flew out to Texas, where Cox was making The Rookie, for crisis talks. "I basically went to Texas to end the relationship.

Brian knew it. He knew something was up.

But when we had dinner together we had a wonderful conversation. I said, 'We're stuck. I'm not happy living with your assistant in London while you sporadically visit. The one thing which ruled my life, my career, is gone. What do I get?'

"We decided we had to either go apart or come together in a different way. So we said, 'Well we could get married!' and we laughed. But then we said, 'Well we could get married.' And we got married three days later. Orson was conceived and it changed our lives overnight. All my doubts that this was the right choice were gone. It was magic time. Rather than seeking for my life in characters and films and plays, I started to have a life and a family, and find value in being me and living my life rather than having to prove I have the right to be here."

She has continued to act, although not as much as before. The reason Cox and Ansari are in London, rather than in Los Angeles where they spend most of their time, is that they are both appearing in Rock'n'Roll, the new play by Tom Stoppard.

They also have roles in Deadwood, the brilliant American television series.

What's it like working together? "Very comfortable, " says Cox. "You couldn't ask for a better situation. It's very relaxing, not at all tense-making." They are each somewhat in awe of the other's acting skills. She calls him as "a master", he commends the "joie de vivre" of her performance. This reminds me of something he said when I interviewed him in 2001. He had recently learned that he was going to be a father and was basking in his relationship with Ansari.

"I'm not very good on joy, " he said. "It's the one thing that I haven't got in my background. So it's nice to be with someone who understands a lot more about joy."

Cox's background was famously grim.

When he was nine, his father died of cancer, and subsequently his mother suffered a mental breakdown. She was given electroshock treatment and was never really the same woman again.

However, he now has a slightly revisionist view of his upbringing. "The truth of the matter is that I had a lot of joy as a kid, " he says. "When I was a very young boy, joy was very much present. My childhood was tough, but the initial state was very enjoyable. Before my father passed, before my mother went nuts, before all of that it was pretty great. That's what makes me, at the end of the day, an optimist."

The renewal of their marriage vows, which took place last month at Birkhill Castle in Fife, was a joyful occasion. Ansari arranged it to coincide with the celebrations of her husband's 60th birthday. When they married in 2001 it was a sudden elopement to Las Vegas, just the two of them, so they thought it proper to have a public acknowledgement of their love. The celebration was widely reported as being Buddhist, however it also contained elements of the native American and ancient Celtic religions, as well as Catholicism, the faith in which Cox and Ansari were raised.

They consider themselves spiritual people, though their belief system is nondenominational. She seems to have influenced him in this, although they share underlying values and are appalled by the hedonistic excesses of Western society. "We live in a world now where people are so about shopping and buying and taking and what have you, " he says.

Cox recounts a recent incident which sickened the couple. They were being driven home from the theatre along Charing Cross Road. In front of their car was a double decker bus full of drunk young women.

Behind them was a fire engine. The women were exposing themselves to the firemen, crowds of young men on the pavements were "flocking like rats" to the doors of the bus and had to be restrained by police.

Meanwhile, the Muslim driver of their car was putting down the visor and trying to prevent his passengers from seeing what was going on. "I was more concerned about him, poor man, " says Cox. "He had to witness this. It was very ugly, and you realise that in today's age, people are very rudderless and without purpose."

His wife takes up the story. "The driver comes from India and sees something like that, and he might go and say, 'Western women are all whores.' Well they certainly have behaved like whores. But whores are actually more honorable because they get paid; it's a job and they pay their bills."

Cox and Ansari find comfort and retreat in raising their children and in work; the theatre is their hermitage. They are finding being in the same play very stimulating;

sometimes they get home from the theatre and stay up until 2am, talking shop.

When Cox talks about acting it's worth listening. He's always ready with a bon mot like, "Actors are transistors for all of human failing and all of human aspiration, and that's what they have to tap into a fairly constant level." He has had a remarkable career, making a name for himself as the first incarnation of Hannibal Lecktor in the cult 1986 movie Manhunter, and going on to appear in a string of high-profile blockbusters, including Braveheart, The Long Kiss Goodnight, The Bourne Identity and Supremacy, X-Men 2 and Troy. His latest project, The Flying Scotsman, the biopic of cyclist Graeme Obree, opens the Edinburgh International Film Festival tomorrow. Forthcoming movies include Running With Scissors, based on the bestselling book by Augusten Burroughs, and David Fincher's Zodiac.

It has been said that when Cox turned 50, having played every major role in British theatre, he vowed to conquer Hollywood.

Was his plan really so explicit? "It wasn't, although that's what it looks like now. But I had always wanted to do films. When I was a wee boy I loved the movies. Although my love wasn't the theatre, I grew up in the tradition that you go to drama school and learn about theatre and become part of it - But I knew I had an appointment to keep with cinema and so I decided that I would reinvent myself in some way."

In 1986, his vaulting ambition caused the end of his marriage to Caroline Burt, with whom he has two children, Alan and Margaret, both now adults. He was too willing to be away from home making his name to pay sufficient attention to his family. Does he now have the balance right?

"I don't know if I've got it balanced but I am certainly trying to balance it, " he says. "I am a compulsive worker. I suppose I still have the fear of poverty. That is something which is deep in me and would take a lot of analysis to sort out. It goes back to my roots and what happened with my family."

When his father died, it was discovered that he was in debt, partly as a result of an investment that had gone wrong. The shock of this and strain of trying to bring up children in poverty sent his mother mad.

"So one is slightly driven by trying to avoid that particular fate - Nicole quite rightly says to me, 'You have to stop worrying about earning enough money.' That's where her faith works well. She has trust. I try to but I'm not really trusting. It's that Celtic thing - we're a defeated people and we're supposed to be defeated. It's in the DNA."

Neither Cox nor Ansari feel secure in their success, but they have learned not to base their sense of self-worth on how their careers are going. "If you don't have something in your life other than acting then it ultimately will ruin you, " she says. "You have to find a centre in your life that is not based on your next job. Because the next job might not come or it might be a flop."

HER husband nods. "That's why I feel incredibly blessed, especially at my age, to have a young family, " he says. "You are having to deal with nappies and poo and whether the little one eats properly. It keeps you sane and real." Given that he has admitted to making mistakes with his elder children, how did he feel when he learned he was to be a father again? "I thought it was a second chance and I wondered whether I could handle it." As it turns out, he is revelling in fatherhood, although his wife has to keep reminding him not to talk to the kids as if they were adults.

What to make of Ansari and Cox? They are a couple of square pegs who seem a good fit for each other. Both are smart and independent, much given to analysing the world and their place in it. She has a very low boredom threshold which has caused her to work across Europe and America, bouncing from job to job, finally finding contentment in her children. His restless nature has brought him much success and some loneliness, and while it's overstating things to say that he has now settled down, his values have certainly tilted towards the domestic. It helps, of course, that he has a home in which work is held in high esteem.

"We give each other a lot of freedom, " says Ansari, "because we know what it takes in order to create."

In October 1990, Cox noted in his diary that his existence had no shape or purpose, that he had sacrificed his life to his career, and that his future seemed more uncertain than at any other time. He was in a rocky relationship, playing King Lear was exhausting and unsatisfying, and he was even missing performances. He couldn't have known that later that month he would meet Ansari, and admits that he would have found it hard to believe such a positive and important encounter was just ahead.

"I was in such a state that I couldn't see any further than the end of my nose, " he says. "But the truth is that you cannot ever ever write yourself off. Once you've bottomed out you come back up. And it's certainly true that meeting Nicole precipitated the start of a revival."

He says, though, that it's important not to take anything for granted. Around the time he and Ansari started to see each other, he learned not to rely too much on either work or personal relationships. "I really believe that you are responsible ultimately for your own misery and also for your own joy, " he says. "Nicole has given me an enormous amount, that's unquestionable, but I wouldn't make her responsible for being the source of my happiness. That's an awful responsibility and not fair. You have to have a sense of separateness, a sense of who you are. You have to stand in your own light."

Brian Cox and Nicole Ansari are in Rock'n'Roll at the Duke of York's Theatre, London, until September 23. Deadwood is on Sky One, Thursdays, 11pm. The Flying Scotsman is at Cineworld, Edinburgh, tomorrow, 9.30pm and 9.45pm