In the new episode 'Homer Simpson, This Is Your Wife', Homer volunteers to take part in a reality show on TV in which he swaps wives with an Englishman, Charles (Gervais), a gauche office manager unhappily married to a domineering, prissy university professor. So Homer gets to share his life with the professor, who burns his underwear and tries to stop Bart watching TV, while Charles is thrown together with Marge, with whom he quickly becomes besotted, even serenading her with a love song.

Gervais conceived the storyline after meeting Matt Groening, the creator of The Simpsons, and Al Jean, the show's head writer and executive producer, shortly after he won a Golden Globe for The Office in January 2004. Groening was a fan of The Office, and hearing that Gervais was devoted to The Simpsons, engineered a get-together. At first the idea was that Gervais would merely lend his voice to an episode, joining an already stellar list of guest stars. But then Groening went one better: might he be interested in writing one?

Brian Viner: Ricky, what went through your mind when you were invited to write for The Simpsons?

Ricky Gervais: Well, I knew I had to say yes, but fear kicked in at exactly the same time.

Matt Groening: That's the way we felt too.

RG: What I think happened was this: they keep being offered more seasons of The Simpsons, and they're very jaded, and bitter that other programmes are even on the television. So they thought, "Let's show that little shit that it's not as easy as he thinks."

Al Jean: Actually, he won an Anyone Can Write A Simpsons Script contest.

RG: Yeah, I sent in my best drawing of Homer, with a letter saying "Dear Homer Simpson, I am nine years old and dying. Can I meet you?"

BV: Had you ever entertained the idea before you were asked?

RG: In all honesty, when I got into comedy in about 1999, I remember thinking that I would love to get a joke on The Simpsons. The thing is, every comedian worth his salt, his favourite thing is The Simpsons. The contest for the rest of us is to come second, first place has already gone. I'm just in awe of it. It's wickedly satirical, and when it nails a joke, then that joke is done, forget it, because it does it in fewer words than anyone can. Also, it's got heart. I love the family unit, the stability of Marge and Homer's relationship. And, you know, the longevity of it. I got out of The Office after 12 episodes because I knew the quality would go down. They've done 400 or something. . .

AJ: We've just recorded the 388th. . .

MG: We love Ricky's work as well. We love Extras, we love The Office, and we are aware of Flanimals.

And the podcast is fantastic. It's dangerous to listen to while driving because it's so funny.

RG: That's a nice quote. Can you cut the bit where I say nice things about them, so it doesn't look as if I'm fishing for it?

BV: Okay, and let me ask you an important question: what was the money like?

RG: It was fantastic. It was nice to be paid cash, and in totally untraceable notes as well. I was very excited to get 5,000 lire.

BV: Matt, when did you first become aware of The Office?

MG: I was flying on Virgin, and watched a bunch of British sitcoms. The Office blew me away, I couldn't believe it. I didn't think it would be successful here, though. I thought it was too subtle for American tastes. Boy, was I wrong!

AJ: So by the time Ricky won the Golden Globe, we were big fans. We really wanted to meet him.

RG: We had this lovely lunch where I showed off and quoted The Simpsons to everyone to show what a fan I was. It's the only thing that turns me into a nerd, that and Spinal Tap. And at the end, as I was getting Matt to draw me, like some tourist, he said, "So, do you want to appear in an episode?" I said, "What are the hours?" He said, "The hours are really good." And they are. They get the actors for 35 minutes a week and they're looking at their watches after 34 minutes. No, that's not true.

MG: No, that is true.

BV: Right. So Al, what did you think of Ricky's first draft?

AJ: It was very funny. He's a great writer, and the song was terrific.

MG: We could never have written his character the way he did.

RG: I must say they're bigging me up a bit too much here. I can't stand it. I feel like I have to confess that I cheated on my exam. The truth is that it was a co-write. I put some ideas down, sent them off to Al, a big bag of jumbled-up stuff, and they put it through their mill. Then they came back to me and said, "Did you mean this?" And I went, "Yes, exactly."

MG: For what it's worth, Ricky, that's the way all our scripts are written. You deserve credit for the script. We tweaked some things, that's all. Like we call them trucks here, not lorries. . .

BV: So a few Anglicisms needed changing into Americanisms?

AJ: Yeah, we took out a lot of references to Yankee bastards.

RG: It's so funny. Someone asked me if it was hard writing for the American version of The Office. They said, "What's it like with the language barrier?" I said, "I'm bilingual. When I came here I only spoke English, but now I speak American."

BV: Your character in The Simpsons is essentially Brent, isn't he?

RG: Thank you for pointing out that I have a very, very limited range. Yeah, there's a lot of Brent in there, but he's a character in his own right. A bit of a loser, a bit of a putz. It was nice to do that again.

I do miss him. But we were doing the read-through, and the other actors, like Hank Azaria and Harry Shearer, were interrupting themselves to do other characters, and I'm thinking, "I'm going to do my weedy little homage to Brent in a minute, to show how versatile I really am."

BV: Was it hard for you and Al to hand over your precious characters to Ricky?

AJ: No, because what's great about this show is that it's so broad - there are so many characters, so many ways you can go.

MG: And we try to surprise ourselves with every episode. So having Ricky on the show was a real breath of fresh air.

BV: Do you ever think The Simpsonsmight be running out of steam?

AJ: Well, we've been picked up for two more years, and the feature film is coming out worldwide on 27 July 2007. I can tell you that the guest stars include Albert Brooks, Minnie Driver and Erin Brockovich, so now you can figure out the whole plot. Meanwhile, the numbers here are still terrific. Ricky's episode won its time slot, and got the highest numbers for three months.

MG: The fans loved it. We got great fan reaction to that one.

BV: To return to The Office, does it bewilder you that there were only 12 episodes made, given how many episodes you churn out in America?

MG: A lot of American shows don't last for as long as 12 episodes. They get cut after one. But certainly one of the great things about The Office in particular was that there was a beginning, a middle and an end. With those two Christmas episodes as the epilogue. But if you recall, Ricky, when you first met us I begged you to do more episodes.

AJ: And I think Ricky begged you to do fewer episodes of The Simpsons.

MG: I just wanted to see what happened to David Brent. I wanted to see him going from job to job.

RG: I think about that sometimes.

MG: It would be so great, people would love it.

RG: The problem is, I have such a big mouth. I've shouted myself into a corner saying there won't be any more. I can't come back now.

MG: I think you would be forgiven. We forgave Johnny Rotten.

RG: Okay, yeah, what about Brent as a ghost? It starts at the funeral, then he appears from behind a tree in a white suit, and whispers in Gareth's ear.

He says, "Don't look now, Gareth, but I'm a ghost and I actually solve crime." How about it?

BV: What did you guys learn from each other, during this project?

AJ: I learnt that you should always be yourself.

MG: That we could stay true to The Simpsons' sensibility, with high-velocity visual gags, but also honour what Ricky does with subtlety and nuance.

AJ: Yeah, there was a scene with Ricky and Julie Kavner [who plays Marge], which was longer than scenes we normally do, and slower-paced, but it got a bigger laugh. . .

BV: And finally, Ricky, now that you've fulfilled the burning ambition to work on The Simpsons, what else is left?

RG: I want to get all the nations of the world together, it doesn't matter what colour or creed, and I want to sit them down and say: "Guys, The Office is still available on DVD."

'Homer Simpson, This Is Your Wife' is on Sky One at 6.30pm on Sunday 23 April