Jeremy: 'Marriage is hard'

I tell him that I can see a pattern emerging. Look at Charles and Sebastian. "It is the same subject matter as in Brideshead, funnily enough. That male platonic friendship, spanning many years. Male friendship is something that isn't often examined. I thought, come on, do it, stop shillyshallying. I always find reasons not to do work."

Has Jeremy Irons ever fallen in love with a man? (I don't leap straight into this question, by the way; we have been discussing the gay western Brokeback Mountain, which Irons is desperate to see.)

"I think I am too competitive with men, that is what gets in the way. I can understand love between two men, I have no trouble getting my head around that. But I have never fallen in love with another man. I have done a film exploring that, M Butterfly, where I was exploring someone who in my subconscious I knew was a man.

"Gender is very interesting, I explored all of that in my head." (He later brings up the lack of chemistry between himself and the French actress Juliette Binoche during the filming of Damage. "It was a tricky time in her life. She had just come out of a terrible relationship with a film director who put her through shit, and so she was really anti-men, not a good place to be if you have to make that film.")

He is disarmingly honest about the movies he has made: the soon-to-be-released Casanova "doesn't bear much examination; Sienna Miller is sweet but inexperienced", although Heath Ledger is "a darling man"; M Butterfly is "a very flawed film"; he "wasn't happy" with Damage. All of which shows he isn't vain, although when I ask him what his most annoying character trait is he says, "Selfishness. I can be very egotistical, I don't nurture friendships in the way I should. I don't ring. I don't write."

I tell him that, like many artists, he must be hell to live with. "Plus, I'm a Virgo," he says cheerfully. "Very anal, very tidy." He likes to spend time in the castle in Cork he has spent the past few years restoring. He is flying there tonight; his record is three-and-three-quarter hours, door to door, from his house in Oxfordshire.

His wife of 27 years, Sinead Cusack, is there at the moment, although they are "not afraid of space. I have a huge need to be on my own sometimes, shut off, even with Sinead. She used to think it was something she had done; now she understands it is just me. I've never been the life and soul of a party."

How do they manage to have such a successful marriage? Does he still look forward to seeing her after a couple of days apart? "Of course. I find her more beautiful now than I ever have. It is extraordinary when you have been with someone that long, you become part of them, they become part of you - you have been through so much together. It's wonderful. We live in a throw-away society. I am a mender, always have been, it drives Sinead mad."

Did they ever think of ending it? "We would have huge rows and think, oh god, but soldiering on is the best advice I would give anybody. Every time you get through a difficult period you come out stronger. Have I been unfaithful? I never talk about these things, I sometimes make jokes. Sinead says, don't talk about it at all."

I tell him I doubt any man can be monogamous. "I think that is a generalisation, everyone has to make their own mind up. What I have learned is that no marriage is what it seems. I will say that is is very difficult to be everything to one person. I don't think women can live with a man who is always having affairs; it can become like an addiction. I don't believe in therapy to try to stay together. A therapist will always blame your relationship. I believe a couple should always talk to each other, and try to make it work, stick at it. It's worth it."

He and Sinead have two sons, Sam, 27, a photographer, who is trying to get on the property ladder in Hackney, and Max, 19, who is training to be an actor at Guildhall. Are they close? "The boys are closer to their mother. We have dinner with the boys and their girlfriends, and, yes, we are close. It's tough to have parents who are fairly successful; they never knew us when we were struggling.

"I do regret that neither of us were there for them full-time when they were growing up; their childhoods were not as idyllic as they might have been." They both elected, aged 11, to go to boarding school (Irons, the son of an accountant, boarded from the age of seven). "Perhaps they grew tired of coming home from school and it being just the nanny who was there to greet them."

I tell him he is a weird mixture. He loves to talk about his "art", but loves doing films that pay ridiculously well, and would have killed for a role in Harry Potter or Lord of the Rings.

"Ian [McKellen; he always refers to people by their first name only and most of the time I have no idea who he is talking about] has always wanted to be a film actor, all he wanted was to be me. Now he has become a film actor, he is happier than ever - he gets to stay in glamorous hotels, he gets to travel. As a stage actor you work long hours for not much money.

"My film work lets me live in a way that seems rather wasteful [as well as the Oxfordshire home, and the castle, with four horses, which perhaps explains the jodhpurs, he has a place in Notting Hill]. I have a profile, so it is nicer for me to be in an area of privacy, having a house where you can disappear and be normal."

But he has always chosen the quirky and the plain creepy (Lolita and Dead Ringers, to name two) over the commercial. He is gregarious but he likes to cut himself off in a castle with a moat and fishing and music and no telly. He loves his wife but he also enjoys his space.

Is he terrified about being on stage again? "I am nervous of letting people down and being clobbered, of not being very interesting, I think that's all that terrifies me."

Embers is at the Duke of York's Theatre, St Martin's Lane, W1. Previews from 15 February. Information: 0870 060 6623. Ticket prices: from £10 to £42.50.