At first, I don't notice the figure hunched over the computer in the corner. It's only when I hear the voice – resonant, commanding, with a trace of a Lancashire accent – that I realise that this grey-haired creature, unprepossessing, at least from behind, is Lear and Gandalf and Vanya and Magneto. Is, in other words, Sir Ian McKellen. And when he turns round, he's not unprepossessing at all. His face is lined, but amazingly handsome. His body, in super-hip jeans, turquoise T-shirt and chic little jacket, is athletic and lithe. Mature but modern is the overall impression. Gravitas with a funky twist. The same could be said of his home, an 18th-century house in East London's Docklands, in which he's lived for 28 years. "It used to be like a boat," he tells me, bounding up the first of four staircases, "but I had it gutted." He had it gutted, in fact, when he was in New Zealand, filming The Lord of the Rings. While his life was changing – from great classical actor to international film star – his house was being opened and filled with light. And now, it's flooded with it.
Sitting at the splendid table in his purple kitchen, overlooking a sparkling Thames, we're bathed in light, blinking in it. Sometimes, it explodes behind McKellen's head, like a halo. Sometimes, it turns his ears a deep, devil-like red. "The multitudinous seas incarnadine" you find yourself thinking, as you gaze at the red ears and the shimmering water beyond.
But then you can't help thinking about Shakespeare when you're with McKellen. You can't help thinking about Lear and Othello and Macbeth. In the past week, I've watched all of them: his nervy, youthful Macbeth, in thrall to Judi Dench's melting iceberg of a Lady Macbeth, his gripping, quicksilver Iago ("the Iago of the 20th century" according to The Times), his Hitleresque charmer of a Richard III, and last year's avuncular, petulant and, finally, spine-tinglingly magnificent Lear.
It's like watching a life, or at least the possibilities of a life. Not the seven ages of man (McKellen's Hamlet, in 1971, for example, wasn't filmed), but a fair few of them. Macbeth was filmed in 1979, Othello in 1990, Richard III in 1995 and King Lear this year. That's nearly 30 years of age and experience, written on a face, on a body and on a voice.
Well, that's what it's like for the viewer (and, over Christmas, anyone with More 4 can be the viewer). What's it like for him? "It's no pleasure," says McKellen, staring firmly down at the table. "I did see Macbeth and it's a little like looking at old snaps of yourself. I know it's good, but when I look at myself in it, all I can hear are lines and inflections I don't like. In Othello I speak too quickly. The performance is fine. The reading is fine. The execution is not. Richard III," he says and then there's a pause. "Terrific." Phew! A just acknowledgment at long last. "But then," he says, instantly qualifying it, "it was a film. More care goes into a film. It's different."
"Terrific" is exactly what McKellen's Richard III is. The only one of his filmed Shakespeares not to be directed by Trevor Nunn, it was based on Richard Eyre's National Theatre production, but directed in the film version by Richard Loncraine, to a screenplay that McKellen co-wrote. Set in a fascist, English version of the 1930s, it's visually stunning, hugely imaginative – part of Richard III's "Now is the winter of our discontent" speech is delivered in an Art Deco urinal – and psychologically fascinating, as McKellen's all-too-believable dictator monarch vacillates between evil and charm.
His Lear, which he did first in Stratford, then in London and then in Brooklyn, interspersed with Sorin in The Seagull, was pretty universally hailed. Michael Billington in The Guardian described it as "majestic" and "moving". Charles Spencer in The Daily Telegraph said it was "destined to be remembered". If Hamlet is the great test of a young man's mettle, Lear is surely the test of an entire career. Was it terrifying?
"It's very difficult," says McKellen, gazing out to the shimmering light. "I think by the time we got it recorded I was as good as I was going to be in the way we were going to do it. But there's a part of me that would like to do it again." What? He's just completed the most harrowing role in an actor's career, to rave reviews, and he wants to start again? Judging from the fingers wrapped around his face, and the body bent forward, McKellen is entirely serious. "I thought there was more I could have done," he explains. "Which actually means less. I could have found a way of doing more by doing less."
And did it feel like the pinnacle? McKellen frowns. "You try not to think about it," he says. "And it was never one I wanted to climb. It's like getting the bus pass. You know you're old enough, but 'it's time you played it' isn't a very good reason. But then, the set-up with Trevor [Nunn], on the road... that shelters you from the sense of occasion that perhaps the critics have... When I played Vanya, the reviews came down from heaven, but practically every time Uncle Vanya is done, the critics love it. But it's the play! You have to sit back and say: 'I didn't get these reviews because I was so, so good.' The play's the thing," he says, echoing Hamlet. "I think we often get over-praised for our contribution, which is just to get up and tell the story."
Gosh. I'm beginning to get a sense of that rigorous Christian upbringing, that son of a lay preacher, who was a son of a lay preacher, that family who tried so hard to be modest and good. McKellen went to church in Burnley as a child, but at 14 he started visiting other churches and "didn't much like" what he saw. Instead, after a first trip to Peter Pan when he was three, and a first performance in a church play when he was seven, he sought solace in the theatre: as a teenager at Bolton Little Theatre, and then at Cambridge, where he read English under F R Leavis, and met Derek Jacobi and Nunn. He started off, in 1961, at Coventry Rep, moved to Ipswich and then Nottingham and then to the National Theatre. In nearly half a century, he has played roles ranging from Romeo to The Magic Roundabout's Zebedee and The Wind in the Willows' Toad. But it's Shakespeare for which he's still best known. Is Shakespeare, I wonder, as near as an ex-Christian atheist can get to God?
"It's reassuring," says McKellen, with that purity of focus which is almost unnerving, "that human nature is redeemable. And yes, there are attitudes that Shakespeare seems to have that explain human life to me. If you want to explore human nature, then read Shakespeare – or better still, go the theatre. Because you'll have your eyes opened. I think my attitude to bad behaviour is informed by Shakespeare's. Shakespeare is fascinated by people who behave really badly."
And Lear? McKellen strokes his face, as if his Lear beard were still there. "There's one thing you understand," he says. "The journey he's going on very late in life is one very worth going on. And one from which he emerges better, and more at ease with himself... It appeals to me as an atheist that he doesn't need to talk to the gods, but to other people. My stepmother," he adds, "died just before I started doing it. She was 100. She had been a Quaker all her life, but when she was 99, she said: 'You know, I just don't believe in God...' I don't think it made her feel any better, but for Lear it makes him feel a bit better. It's quite a good way of looking at old age. The idea that you can get better." So, is he getting better? McKellen pauses, wriggles and strokes his face again. "I'm having a go," he says. "it's hard. You catch yourself out."
He has, of course, been on quite a journey himself. It's 20 years since he came out as gay, during a live radio debate with Peregrine Worsthorne on Section 28, the piece of Thatcherite legislation that forbade the promotion of homosexuality in schools and triggered a wave of gay rights activism. For McKellen, it was like being born again, the perfect conduit for his evangelical gifts. "I'm not often convinced I'm right," he says, "but practically everything I've said on gay rights, I know I'm right. I know better than the people who are telling me I'm wrong."
He was 49. More than halfway through most lives. Does he wish he'd come out earlier? Again, the pause. "Yes," he says, "but I don't know what sort of campaigner I could have been, because I wouldn't have come up with some campaign... I find heterosexuality far too interesting not to have anything to do with it and I couldn't spend my life being in gay plays." But he was brought up to be honest, and for nearly 50 years, he couldn't be honest. That's quite a price to pay. McKellen gazes out to the water again. "Well," he says, "you don't like yourself." And then he adds, with terrible simplicity: "It rots you."
In his 68 years, he has had two long-term partners: Brian Taylor, the drummer with the Tom Robinson Band, from 1964 to 1972, and then, from 1978 to 1986, theatre director Sean Mathias. He and Mathias have remained friends. It was in Mathias's Aladdin, two years ago, that McKellen stole the show as Widow Twankey. In March, he will take on Estragon to Patrick Stewart's Vladimir in his Waiting for Godot. "I think," he says, when I ask what it's like working with an ex-lover, "that he has a direct line to my vulnerability."
Vulnerability. Well, yes. This multi-award-winning star of stage and screen, national treasure, knight of the realm, Companion of Honour and gay icon, has the air, appropriately enough for a man who has played Gandalf, of someone on a permanent quest. "I think my life has been skewed," he says, "by my having a career. I do like domesticity, but I've not been very good at it. One of the things about being an actor is that it's a craft. It doesn't come from nowhere. I relate jobs I've done and I see I've got better. It may not be a child, or a written masterpiece, but there have been sacrifices.
"My mother died when I was 12 and her sister said that she'd always said about me: 'If Ian does become an actor, it would be a wonderful thing because he'd bring such joy to people.' Well," he says, taking a final swig of peppermint tea from a mug, which, I notice, is emblazoned with a picture of Richard III, "that's a simple little notion that I've held on to."
'King Lear' (Christmas Day, 9pm) is the centrepiece of a Sir Ian McKellen and Shakespeare season on More4 over Christmas, which includes 'Othello' (1990), 'Richard III' (1995) and 'Macbeth' (1979). 'King Lear' is available now on DVD