Since becoming the breeches-clad object of so many female fantasies, Colin Firth has gone to some lengths to avoid being typecast. But then, weirdly for a leading man, he really doesn't thrive on being the centre of attention.

Last year Colin Firth moved house. For years he had lived in Hackney in east London which - at an educated guess - perfectly tallied with Firth's sense of who he is: an ordinary Joe, the antithesis of posh, and certainly no card-carrying member of the mover/shaker in-crowd. He remains defiantly scruffy. Not a man to throw on a suit in a hurry, let alone the Regency breeches which he will wear forever in the lascivious fantasies of middle-class English womanhood, he pitches up for the photoshoot in his regulation smudgy round-necked pullover.

But since he married his Italian girlfriend, Livia, in 1997, he has moved to a new address which is more suit than sweater. Barnsbury, where the Firths now live, is at the epicentre of the Islington comfort zone. The difference between the addresses can be summed up thus: "I was sitting in my house reading and two people came past and actually looked through the window," says the house's new owner. "And one of them said, 'Oh look, it's Colin Firth.'" It wouldn't have happened in Hackney. Pride and Prejudice didn't have such big penetration there."

So Barnsbury is where Firth needs to get back to from the photographer's studio in Shoreditch. It's less than a mile away, the traffic will be hell, but Firth wants to take a cab anyway. Unfortunately the one that was booked for him hasn't turned up, so he has to walk. We stroll along the Regent's Canal, which is quiet and uncrowded, but at a certain point he will have to cross Upper Street at its most pell-mell. He doesn't seem to welcome the prospect. Again I could be guessing. I've interviewed Firth more times than he probably cares to remember, and a frequent theme of the conversation is his disputatiousness. I posit some theory about him, and the next time we meet he (politely) remembers disagreeing with it when he read it. I'm relieved to hear that it's not just me who has this problem.

When he was making Fever Pitch, Nick Hornby brought Helen Fielding, the author of Bridget Jones's Diary, on to the set. The Bridget Jones character, at the time, was the nation's leading Darcymaniac. "I felt a little bit shy and clumsy and embarrassed," says Firth. "I felt I was the one making the faux pas and saying the wrong things. She then wrote up a Bridget Jones version of the visit to the set, which is very funny, but didn't echo my recollection, although Nick said it was very close to what had happened. She wrote a thing about having followed me inadvertently everywhere around the set until eventually I said, 'I am going to have to go on alone from here because it's the men's toilet.' I don't remember that. Nick says it's true."

I guess that Firth's fear of Upper Street in rush hour is based on the, "Oh look, it's Colin Firth" syndrome. For a while after Pride and Prejudice, Firth's house in Hackney was staked out by paparazzi, who then followed him out to Rome as his wedding approached. Their pursuit was "very, very unnerving in a way that it's almost impossible to explain to anyone who hasn't had it happen. I was someone who wouldn't have taken it seriously as a threat until it actually happened. But it became extremely important to me that my wedding day was not invaded by paparazzi. We had the Diana experience in Rome of being chased through underpasses on motorbikes at the time leading up to the wedding. That night was the first night I'd decided it was a game, that this could be fun. I felt like I was in a Bond film. But you do get a bit paranoid. I got very skittish about being invaded, and also some of the trickery was unnerving. People phoning up pretending to be British Telecom, trying to get information, and you get this horrible feeling afterwards when you realise it wasn't British Telecom and you've just told them things."

It's years now since Darcymania subsided, but the old wariness is intact. Quite recently he and Livia went to the theatre - Sam Mendes's Donmar Warehouse, to be precise - to see The Real Thing, starring, as it happened, Jennifer Ehle, who was Lizzie Bennet to Firth's Mr Darcy (a relationship that extended off screen). Who should the Firths find themselves sitting next to but those quondam Islingtonians, Mr and Mrs Blair. Firth says that, before the lights went down, he could just feel the eyes of the entire audience waiting for the two parties to acknowledge each other. You sense that he would happily have curled up and died.

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