Don't mention Mr Darcy

Things don't start well with Colin Firth when I recount a colleague's tale of her recent trip to a London members-only bar where the toilets are marked with the words "milk" and "honey" instead of symbols. Uncertain which to choose, she entered "honey", and found Firth behind the door. To her dismay, he apparently made a hasty exit—which seems to be exactly what he'd like to do now.

"Milk and Honey? Me? I don't remember that. I might have done," he winces, shifting in the chair.

The faintest hint of a blush is visible under the whiskers he's still sporting after finishing another film shoot last week. I'd hoped the story might lead to a playful game of words, with Firth choosing between options such as film or stage, love or fight, and pride or prejudice.

(The reasoning being that Firth—aka Mr Darcy—is probably sick to death of the standard promotional trail questions about that scene a decade ago when he emerged from a lake in those britches.) Except he doesn't seem too keen.

Business, or pleasure, I ask?

"Oh, pleasure," he says, showing none. Crosswords or Su Doku?

"I loathe both, I can't bear them," he almost snarls. Tunnels or bridges?

"Bridges. I'm claustrophobic."

Parliament or pressure group?

"Pressure group, definitely," he says, warming to the task. (Firth presented the European Union with a "Make Trade Fair" petition bearing more than 10 million signatures collected by Oxfam International days after the interview.) Hugh Grant or Kevin Bacon?

"Depends on what we're talking about," he says. Given he recently filmed sex scenes with Bacon in the edgy flick Where The Truth Lies, there's plenty I'd like to talk about, but this is a family newspaper, and he's here to talk about a family movie.

We agree to abandon the game and move on to Nanny McPhee. Firth plays the widowed father of seven uncontrollable children who finds a magical woman on his doorstep who whips them all into shape.

The actor says he loved working on the film, despite doubting he was right for the role.

"I'd never done a film for children of this age and I wasn't sure about it.

I usually play the fairly complicated characters and I wasn't sure if I was cut out for the innocence of it," he says. "Once I got over myself a bit, and it took a couple of days, I had a great time doing it."

Firth was especially attracted to the idea of working with Emma Thompson, whose character gets less ugly as the film progresses.

Firth says he wouldn't bother changing anything about his looks.

"I'm quite happy to let the face go where it goes, really," he says.

"We can, if we want, evaporate our facial features. Members of my profession go rushing to the surgeon all the time."

His character fares better than co-stars Angela Lansbury and Kelly Macdonald, who get pelted with pies and cakes during a foodfight.

"What looks a rollicking good time is a painstaking and drawnout process," Firth says. "Those things weren't edible. My children came to the set and saw all these pink and purple buns ... I had to tell them not only would you break your teeth if you tried to eat one, you'd be hospitalised if you succeeded."

A father of three, Firth steers clear of talking about his own brood too much. His teenage son to actor Meg Tilly, his co-star in Valmont, lives in the US. The actor visits as often as he can, spending the rest of his time either in London or Italy with wife Livia and their two young sons.

"Fatherhood turned my life upside down, really. It changes your concept of who you are and what you think your ambitions are. But I'm not going down that route (of talking about them)," he says firmly.

Given it's a kid's flick, will he take the young ones to see it?

"I don't push myself at them. The little ones are very little," he says.

"It's weird to see a parent on the screen and I don't think I'm going to hasten towards that moment.

They've seen me in magazines and on buses, but they probably think everyone's dads are on buses."