You've worked in radio, television and film. Which is your favourite?
The perk of acting is that you don't have any responsibilities apart from remembering your lines loosely. Writing and directing are very stressful but fulfilling. Radio is great fun because it's largely unpoliced. But I would rather sit at home doing nothing other than watching other people's work, if I'm honest.
You do stand-up, too. After all your success, why take the risk?
I used to do stand-up years ago. Recently, I've felt that I've got unresolved business with it. It's a challenge, and I can't hide behind Ricky.
How do audiences respond to you?
They don't know what to expect. I'll get teenagers who like a bit of naughty swearing and then the "retired major general" types who are expecting a Radio 4-style satire. I find that I generally dissatisfy most of the audience.
What's the secret of your partnership with Ricky Gervais?
At the core, it's a shared set of interests and values. We've been working together for 12 years and it's by turns like a marriage and a brotherhood. My suspicion is that we can do stuff apart, but when we do stuff together it will be better. It's got that kind of spark to it.
Did you imagine The Office would be a success all round the world?
Goodness me, no. We didn't think it would get much of a viewership here. I remember us saying we would be happy if it got a small cult audience. It seemed so specific and low-key. But it took on a life of its own.
It's a huge hit in the US. Do you think the TV culture there is better?
I think it's a question of economics. Because they've got a big mainstream TV scene, they can afford to have all this fringe TV that is very experimental. They've got the money to do it.
Are you worried about the future of the BBC under this government?
I'm always worried about the fate of the BBC. We've just made a programme for Sky, but I'm still worried about the march of Murdoch. I do not think the BBC is above criticism; my worry is when the criticism has an agenda.
Are you politically engaged?
I consume newspapers and wake up to the Today programme. But I don't affiliate to a party; I can't subscribe to a doctrine.
What do you make of the Prime Minister?
He presents himself well, but I'll be interested to see what David Cameron does once the paint starts to flake off.
Why don't you do political satire?
It needs someone really informed, like Armando Iannucci, to do it well. I don't have the kind of anger that fuels great satirists such as Chris Morris. I'm more intrigued by, say, those last days of Thatcher - by the emotion in that - than the big brushstrokes.
What draws you to that kind of material?
I'm interested in the everyday, and the idea of big emotions being experienced in seemingly small lives. I don't need to see stuff exploding. The guy who runs the local karaoke night is more interesting than a pop star.
Did your upbringing shape your approach?
I didn't have a father who was a drunk and a mother who worked three jobs - life wasn't really hard. So what intrigues me is those little bits of unhappiness that gnaw away at people.
What do you want to do next?
People assume you can only move forward, as opposed to sideways. The people I really admire, like Woody Allen or Billy Wilder, just follow whatever is interesting to them. I'd love to do a conspiracy thriller one day, or a musical.
In a different life, what would you have done?
I could imagine myself teaching. I like to think of myself as Robin Williams in Dead Poets Society. The kids would thank me when they're winning Oscars.
Where is home?
I still have a soft spot for Bristol, but London's the place I miss when I'm away too long.
Is there anything you'd like to forget?
Not really. I don't feel I've betrayed any people. I haven't done a bank heist. So far I'm sleeping at night, just about.
Is there a plan?
The plan was to try to make a sitcom that you can be proud of, that stood in some people's minds in the way Fawlty Towers did in mine. That, to a degree, came true. Now I'm just making it up as I go along.
Are we all doomed?
Ultimately the sun will burn out or consume us. But I don't think we are doomed because of a lack of God or because of our inherent cruelty to one another. There's enough great stuff in the wonders of the cosmos not to create gods.
1974 Born in Bristol
1997 Becomes Ricky Gervais's assistant at Xfm radio station
1998 Finalist in the Daily Telegraph Open Mic Awards
2001 First episode of The Office, co-written by Merchant and Gervais, airs on BBC2
2005 Their next series, Extras, begins
2010 The film Cemetery Junction is released, co-written and co-directed by Merchant and Gervais