If I learnt one thing from my interview with Mackenzie Crook it is to take Wikipedia with a pinch of salt. The unassuming 37-year-old’s page claims that he is a vegan, yet the first thing he does at our lunch is order a beefburger. Maybe the cyber rumour comes from a pallor that erroneously suggests he has not had a decent fry-up in years.

But then Crook is full of surprises. It is hard to believe that it is nearly a decade since he emerged as the insufferable Gareth in The Office. Though for Crook it is easy to date the desk dork’s debut. “I got married then and we’ve been married eight years.” He even boasts Gareth’s dreaded blond bowl cut in his wedding pictures.

Today, the Kent-born actor sports a sludge-brown look. I assumed that this was part of the find-the-character process for his role in Jez Mojo” Butterworth’s new state-of-the-nation comedy, Jerusalem. Crook plays Ginger, the best mate of Johnny Byron (Mark Rylance), an ageing Wiltshire tearaway. It transpires that the hair is for a previous role in the BBC’s Merlin. By the time we take his photograph, a few days later, he’s gone ginger.

The Office may have been an age ago, but it has recently been on Crook’s mind. The BBC is preparing an autumn Ricky Gervais retrospective, screening every episode. Crook was interviewed for a documentary and has nothing but fond memories of Gervais plucking him from comedy-circuit obscurity, where he was scraping a crust playing the spangly-suited spoof entertainer Charlie Cheese.

“It was my big break. Absolutely. I don’t like to think what I’d be doing if it hadn’t come along. Would I still be doing Charlie Cheese? I know an awful lot of great actors who haven’t had that kind of break.”

Crook likes to return to the theatre to renew his dramatic licence. Last autumn he was the toast of Broadway as the lovesick Konstantin in The Seagull, directed, like Jerusalem, by Ian Rickson, which transferred from the Royal Court. The New York Times praised him, saying that he “self-combusts from stymied passion”. Theatre is the hardest acting he has done, he says. “You feel as if you are actually working for a living, not just mucking about.”

The Seagull closed at Christmas and at the time Crook had an empty 2009 diary. But this hollow-eyed character player, best known to film fans as Ragetti in the Pirates of the Caribbean franchise, seems recession-proof, promptly shooting off to LA to appear in Steven Spielberg and Peter Jackson’s motion-capture version of Tintin. Then it was back to England to do Merlin and play Russell Harty in a forthcoming biopic. Russell Harty? The northern chat-show host? Another Wikipedia wind-up? “No, Russell Hardy, Ian Dury’s original keyboard player in a biopic, Sex & Drugs & Rock & Roll. Andy Serkis plays Ian.”

He may not be playing camp interviewers, but Crook is more versatile than he appears: “I was walking down the street the other day and someone shouted: ‘Oi, Gareth!’ Then later someone shouted: ‘Ragetti!’ Then someone shouted Skins!’, because I was in that recently. I’m really pleased to have done stuff that affects different people.”

Jerusalem is also an affecting work. Bitingly funny and extremely pertinent, it asks what it means to be English at a difficult time. “Why has ‘English’ become a dirty word with connotations with the far Right when it is all right to talk about Scottishness or Welshness?” Crook asks. Jerusalem, set on St George’s Day, explores what it means to be English today. “It’s not a response to the BNP,” he adds. “Jez is just a big fan of rural life. It’s a celebration of that life and the way that it is changing.”

Crook is not completely averse to the rural idyll either, owning eight acres of green and pleasant land in Essex. “Yeah, we’re gonna bulldoze it, tarmac it and build a car park,” he chuckles. “No, it’s protected. Somewhere to take my kids.”

When not hiking through his very own forest, he lives in Peter Sellers’s old house in Muswell Hill, North London. “It’s the place he bought with his wife Anne in 1956. I spoke to his son Michael to see if he had any memories. They moved when he was 3, but he remembered his father changing the kitchen into a darkroom and turning the radiator key and leaving stains on the floor. I told Michael he could come round, but he died about six months later. I wonder whether there were bad memories.”

Crook was hooked on the house before discovering its history. “There’s a huge beech tree at the bottom of the garden that Sellers planted. The neighbours want me to chop it down because it casts a shadow over their gardens but I won’t. I like the fact that he is pissing off the neighbours from beyond the grave.”

Jerusalem is at the Royal Court, London SW1 (020-7565 5000; www.

royalcourttheatre.com), from Wed

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