The new production of Noël Coward's Private Lives may represent Toby Stephens' acting debut at Chichester but it's a theatre he knows well from his days working as a teenage stage-hand in the 1980s. Although Toby, as the younger son of Sir Robert Stephens and Dame Maggie Smith, was almost born to be an actor, he was still undecided about his future career after leaving school and so a job backstage at Chichester seemed the ideal short-term option. It was, he says, a very valuable experience.

“It taught me the importance of being nice to everyone," he says.” And I came to appreciate that everybody, not just the actors, has a part to play in putting on the show. Some of the actors, often the younger ones, could be a bit off-hand with us and stuck-up. But I remember it as an idyllic time and it left a mark on me. I also remember several stage-hands coming up to me and saying that they'd worked with my father and that he'd been really kind to them."

Toby's parents were a memorable Elyot and Amanda in their day and yet their son, ideal casting for Elyot, one would have thought, reveals that he had to be persuaded to take on the role.

“I’d never thought of myself as an Elyot and, to be honest, I never really liked Coward's plays. I'd seen quite a few of them and I felt that they were all affected and that you always knew you were watching a Noël Coward play. Jonathan {Kent} suggested that I read Private Lives and I was genuinely surprised by how moving it was - how much it is a play about love. Elyot and Amanda have a love that is real but which is also impossible; the chemistry they create is both wonderful and explosive. I also felt that there was a kind of sadness about them, especially in the way they are constantly trying to escape from reality."

Toby was also drawn by the idea of staging the play in the Minerva Theatre rather than in the main house.

“I’d been talking to Chichester about doing something for the fiftieth anniversary season but nothing they suggested had much appeal for me. Then Elyot came to mind and I thought that I'd better play him before I got too old. I also felt that it would be really interesting, simply to have these two people in a room talking with the audience looking into this relationship from close quarters."

Toby points to Elyot and Amanda's wealth, a happy situation which allows them to spend their time as they choose - the idle rich, indeed.

“They appear to behave in a superficial way but at times the mask of superficiality slips and you see how this pose is a defence against the world. What they suffer from is boredom and boredom can be a terrible thing. It forces their energies back on themselves. Elyot is desperately trying to get some control over his life. He's trying to conform and he tells himself that he will find a sensible wife. He's also gone round the world in the five years since the divorce and I think that there's a part of him that had hoped Amanda would still be available."

In the role of Sybil, the "sensible” wife is actress Anna-Louise Plowman, perhaps best known for her recurring character in Holby City and in private life, Mrs. Toby Stephens. This is the first time that have appeared together on stage and since the couple have three children under six, a spell in the Sussex countryside en famille must have seemed like the perfect situation.

"It's very nice to be working together, although, since Elyot and Sybil have only just got married and so there's a physical unease between them, we've had to unlearn the short-hand which we've developed as a couple. It's also nice that we can come home after a day's rehearsal and talk about how it's gone. In a way, I'm glad that Anna-Louise is playing Sybil rather than Amanda. I think that it must be a very risky business for a married couple to play Elyot and Amanda. The play is very close to the bone at times and it is such a bare-knuckle fight between them that it might be dangerous for the strength of the off-stage relationship."

For both Toby and Anna-Louise, the speedy arrival of Eli, Tallulah and Kura in quick succession has understandably been a transformative experience which has been far from easy.

“I do find it a struggle," Toby admits. ”A massive change takes place in your life when you realise that you are no longer the most important person in the world. Flying with them all to New Zealand one Christmas was just hell for twenty-four hours but now that they are growing into people, with their own characters, it is getting better. Eli knows that I pretend to be other people but they don't quite understand that it's work and we'd like them to appreciate the value of work as soon as possible!"

With family responsibilities in mind, Toby has to find a balance in the jobs he chooses to do between what pleases him and what will pay the mortgage.

“It’s a real problem," he says.” You can't be too picky anymore and at times you have to swallow your sensibilities and go for the money. On the other hand, it's quite good for you; it stops you indulging yourself. There's something quite healthy about the need to be pragmatic."

Given their ancestry, it wouldn't be a complete surprise if at least one of the Stephens brood decides to join the family business. Their father has mixed feelings about the prospect.

“There’s a bit of me that wants them to do what they want to do. But acting has never been a secure profession and I'd worry for them if they wanted to go into it."

Toby has a couple of films in the pipeline. He singles out All Things To All Men, a thriller with Gabriel Byrne and Rufus Sewell, and The Machine which he describes as " a mixture of  Frankenstein and Metropolis. I play a slightly unhinged scientist who has lost his moral compass. We shot it in only four weeks: I hope it works out."

Private Lives plays in the Minerva Theatre 21 September - 27 October.