Stiller calls in an Extra favour. . .

Stiller and Gervais are friends following the American stars' cameo on Extras, so this time round he sent the British actor an email asking him to return the favour.

"I wouldn't have thought it was something I would do - a Hollywood blockbuster," says Gervais.

"But I'm not a film snob," he says. "I much prefer a good blockbuster to a thought-provoking art-house movie - because entertainment is where it's at.

"This film doesn't skimp on the comedy, it has got heart, and it's visually amazing."

Gervais acknowledges that everything he has in career terms in the US comes from The Office and its cult status in America.

"I think it was the highest rated show on BBC America, but it was only getting a million and a half viewers across the US," he explains, "but about half a million worked in Hollywood.

"We thought, Why don't they put their money where their mouth is?

"So we approached people we knew had said their favourite show was The Office, and they said yes'.

"If Extras had been awful or they had a bad time you quickly use up your good will," he concedes. "But I still feel that they're doing me a favour and I'm always grateful." Courteney laughs last

Despite having become a household name on Friends, Courteney Cox, below, says she used to think she had no sense of humour.

Cox provides some of the comedy relief in Zoom, a superhero comedy starring Tim Allen, but insists she is not a natural comic.

"As a kid I didn't feel like I fitted in," she says, "because I didn't think anything was funny. All my friends thought everything was really funny and I didn't. So it was really a big thing for me to learn to laugh."

Although her Zoom co-star Tim Allen has no plans to return to TV, where he starred in Home Improvements, Cox has no qualms about another small screen series.

She has just starred in Dirt, a series for the FX cable channel, playing a tabloid journalist.