Martin Freeman is camera shy. The impish dirty-blond actor is standing awkwardly in an old-fashioned hotel library flashing a non-smile towards a photographer.

"I wish I had that talent of being able to accept a photograph being taken," he says, apologetically.

Almost 10 years since the role of Tim Canterbury in The Office made him famous, Martin still doesn't behave like a 'celebrity'.

You'll never catch him being papped at a nightclub or parading his two children in Hello magazine.

"I don't like it when I see people do it. I don't think they should be put in prison or anything, I just think that's not for me because I've never wanted to trade on anything else other than work. I'd rather be at home."

Equally, the 38-year-old's not about to appear in a reality TV show.

"What I try to resist is doing stuff that I don't want to do, just to get on telly. But if someone says, 'Do you want to go to Detroit and make a thing about Motown?', I'll do it because I'm interested in that.

"Or 'Do you want to have your picture taken by [celebrated photographer] David Bailey?' - I hated that as well," he laughs. "But you go, 'Alright', because that won't happen very often. But if it's, 'Do you want Hello to come in and meet your children?' - 'No'."

Whether he likes it or not, Martin is now firmly back in the spotlight, promoting his new film Nativity!

He plays frustrated-actor-turned-primary-teacher Mr Maddens, who is tasked with putting on the nativity play and beating the rival posh independent school to a five-star review in the local paper.

But having been being dumped by his girlfriend Jennifer (Ashley Jensen) five years ago, Maddens hates Christmas. Struggling to cope with the nativity task, he accidentally boasts to his rival that his ex-girlfriend, now a hotshot producer in LA, is coming over to film the nativity play.

Ignoring the old adage about never working with children and animals (in this case camels, donkeys and sheep), Martin threw himself into the film, which was conceived and directed by Debbie Isitt and entirely improvised.

"I loved the idea. I'd worked with Debbie before on Confetti and we had a meeting back in December 2007 about her next idea - she just described the outline of my character and his journey, and I was hooked.

"She has a good way, even just one-to-one, of telling a story, not showily but really enthusiastically. She said, 'It has to be you Martin' - she's very good at flattery, and she has a very popular touch. She has no shame at all about loving children's films, and it's quite infectious."

Martin enjoyed the freedom of being able to improvise.

"Debbie's general MO would be, 'We need to get from this point to this point by the end of the scene, away you go!'. How you get there is down to you, but you have to hit certain landmarks along the way. I think Debbie likes the uncertainty of what can happen in a moment."

With more than 30 kids in most scenes, there was plenty of uncertainty - and Martin's convinced some of the children didn't even know he was an actor.

"For grown-ups it's easier to understand that we've got other names that we call each other, but some of the younger children weren't sure if I was an actor or if I was their teacher - some of them thought of me as Mr Maddens."

Being mistaken for a teacher had its advantages though, especially when it came to disciplining the kids.

"I was able to draw on being a dad and speak sternly, or occasionally go ballistic," he says.

Another draw of the film was the opportunity to work with Ugly Betty and Extras star Jensen.

"I had met her before because I know her husband [actor Terence Beesley] - I didn't know her very well but I felt like I knew her because we had people in common."

Martin admits the pair swapped notes on Ricky Gervais, their co-star in The Office and Extras.

"She was what you'd hope people should be who are doing something for a living that they really love. We should be quite nice, you shouldn't be a prick, because actually you're getting paid to do something you really enjoy."

It's impossible not to ask Martin whether he ever starred in his own school nativity play, as a child, but he insists he can't remember ever being in one.

"I was at a Catholic school so there would have been nativities happening - I remember a lot of Christmas stuff, a lot of Mass and jollity, but I don't remember being in a nativity."

His own children are still too young to play Mary and Joseph - Martin politely declines to give their names and ages - but he's very keen to bring them up knowing the nativity story.

"I always go for an Advent calendar with religious people on it as opposed to snowmen. I think whatever society we are now, we have the date for a reason.

"Regardless of whether you're a believer and whether you dig it or not, this culture is where we come from, so it's just good to know stuff.

"It's still my favourite story, I can't think of a better one. It's a lovely story to tell your children, and I want them to be included in that.

"I'm not heavily religious, they can do what they like, but I want that to be present, and I certainly want it to be present at Christmas - it doesn't negate the fun stuff.

"This film is certainly not heavy or religious, but it's got some levity to it. Despite all the High School Musical side of it, there is feeling. The story is still told, just with a bit more rapping, you know?"

Martin was born the youngest of five children, in Aldershot, Hampshire. He grew up in the suburbs of London and attended the Central School of Speech and Drama.

His acting career began on the stage, and he had roles in The Bill and This Life before The Office changed everything.

But he's adamant that there should never be a reunion of the award-winning sitcom, which ran for only two series.

"I think it would be a mistake, and I trust Ricky and Steve [Merchant] not to have to go back. Unless you've got a fantastic reason for doing something, it always feels a little bit to me like an admission of failure or desperation," he says.

"I always thought a huge part of the appeal - apart from the fact it was a huge show that I'm very proud of - was that it ended. And no matter how much people think, 'Oh we want more', I always think, 'You don't really'.

"If we did five more series, by series four you'd be thinking, 'Oh, it's not that good anymore', because that's when that starts to kick in. You can't level that at that show because there's not enough of it. It doesn't have a big drop-off in quality."

In the New Year, Martin will be filming for TV once more as Dr Watson, in a modern-day version of Sherlock Holmes for the BBC.

He's not going to watch Jude Law's version in Guy Ritchie's latest film, which stars Robert Downey Jr as Holmes, or any other adaptations for that matter.

"If you're over 20 in this country, you've grown up knowing Sherlock Holmes as part of our shared culture. I'd never read any [Arthur] Conan Doyle before doing this, but what strikes you is that my character wasn't written as bumbling, he was an army doctor invalided out of Afghanistan in 1880.

"So for this one, it's set in London now and I've just been invalided back from Afghanistan, so the parallels are there, hopefully without being too anachronistic."

He's also just finished work on film comedy Swinging With The Finkels, but unlike his Nativity! co-star Ashley, Martin won't be moving to Hollywood anytime soon.

"It's an ongoing conversation I'm having with myself and the people around me. I have very good representation there, but I have more considerations now I've got the family. I can't just go 'Bye', and I don't want to either. I love home - and I'm obviously at a different level there, it feels like starting again.

"I would love to work there, but then I'd love to work anywhere there's something I want to work on. It has to feel really right, and I certainly don't want to be working like a slave at a bloody TV show all year in another country, no way."