TORONTO - For Ricky Gervais's directorial debut, the British comedian has tackled a high-concept comedy about a world with no lying that features a glittering cast, a subversive message about the nature of truth and potentially controversial ruminations on religion.

Pretty ambitious, huh?

"It's probably a bit more ambitious than usual really because we had the high concept but we didn't want that to just be an extended sketch," Gervais told The Canadian Press in an interview in a Toronto hotel room.

"But you play to your strengths -- and my strength is being a fat, chubby little loser."

That's the sort of devastating self-deprecation that Gervais withstands again and again in "The Invention of Lying" -- which opens Friday.

The film, which Gervais co-wrote and co-directed with newcomer Matthew Robinson, takes place in an alternate universe where no one is capable of lying.

Gervais plays Mark Bellison, a lifelong loser and failing screenwriter who loses his job and soon afterward, faces eviction from his modest apartment. Feeling desperate and on the verge of destitution, Bellison tells the world's first lie in order to squeeze some money out of the bank and keep his apartment.

From there, he realizes that since everyone will believe everything he says, he can do pretty much anything he wants.

"I wanted to really track what a loser would do with this power," Robinson said.

Added Gervais: "Mark's a putz that you want to win. You're watching an underdog get lucky because he deserves it, it's as simple as that."

But the film really takes off in the fully fledged development of its quirky concept.

This is a world where discussions of depression and suicide comprise idle elevator chit chat, where cops speak freely about their racism and corruption and where a Coke commercial consists of a desperate-looking pitch man in a white room, confessing that the soda is "just brown sugar-water" that will make you fat ("I'm Bob, I work for Coke, and I'm asking you to not stop buying Coke").

Jennifer Garner plays Gervais's love interest in the film. On their first date, she cheerfully discloses painfully intimate details of her sex life and informs Gervais in a matter-of-fact manner that she's out of his league. Their waiter, played by Martin Starr, confirms this, and also notes that he took sips from each of their drinks.

Rob Lowe, meanwhile, is cast as Gervais's nemesis, Brad Kessler. Kessler is a monstrously successful screenwriter, but since it's a world without fiction, his biggest hit is a film about Eli Whitney and the invention of the cotton gin.

Lowe is also Gervais's primary competition for Garner's affection. But relationships in this universe boil down to selecting a mate who is physically attractive and well-to-do, and Gervais, we are told again and again, just can't measure up to the svelte Lowe.

Lowe and Garner master a sort of wide-eyed naivete, maintained even as they deliver witheringly cruel lines to Gervais, who takes a constant beating for his weight and the shape of his nose.

By contrast, Lowe is held up as the perfect biological specimen -- which he says he took as a compliment.

"If only Ricky knew the aches and pains," Lowe said with a laugh.

Meanwhile, the film also gives Gervais the opportunity to take a few digs at organized religion.

At one point in the film, Gervais's character tells his ailing mother a fib about where people go when they die -- a falsehood that spreads like wildfire to hopeful people around the world.

Soon, he has hundreds of people camped out in front of his apartment hoping to hear about the "man in the sky" who doles out mansions to people who die after leading good lives. He even writes a list of rules -- hastily scribbled on the inside lid of a Pizza Hut box (Gervais swears this wasn't product placement) -- for the paths to reaching paradise.

While Gervais says he's an Atheist, he maintains he had no intention of offending anyone.

"I suppose Mark sort of invents religion, but again, it's not a preachy film," Gervais said. "I hope it's not propaganda."

The movie features a never-ceasing parade of celebrity cameos, including Tina Fey, Philip Seymour Hoffman, Jeffrey Tambor, Jason Bateman, Christopher Guest, Jonah Hill and even Edward Norton, cast as a manic, moustachioed, cocaine-huffing police officer.

"Ricky is, at this moment, he's like Woody Allen in 1979 -- he's the arbiter of comedy," Lowe said.

"Everybody understands that he, at this moment in time, is the auteur. So you're going to be in a Ricky project no matter what the part is, no matter what the script is. And then, in a happy accident, the script was actually really good too."

Said Gervais: "We pinch ourselves that I've got this access. It's all 'cause of 'The Office,' really. I know that."

Gervais describes the film as "'Back to the Future' meets 'Groundhog Day' meets 'The Apartment' meets 'Sleeper,"' and the connection that the endlessly personable star feels with the material is palpable.

It's somewhat surprising then that Robinson actually wrote the original version of the script on his own.

He was a fledgling writer in Los Angeles who penned the part specifically for Gervais, never actually thinking that Gervais would even see the script. But a mutual friend brought it along to a lunch date with Gervais, he read it, and immediately called Robinson.

"I was at Grauman's Chinese (movie theatre) at 11 a.m. on a Friday, because I'm an unemployed writer, watching 'Grindhouse,' and I accidentally left my phone on," recalled Robinson with a laugh.

In other words, his good fortune mirrored that of his main character.

But Mark Bellison's meteoric rise to celebrity and riches doesn't actually do much to make his life better. Gervais similarly insists that his life hasn't really improved that much since "The Office" launched in 2001 and became an international sensation.

Honestly.

"I'll tell you something, if you look at my happiness, the only thing that's made me happier in the last 10 years is the sense of achievement and pride in my work," he said.

"I've always had a good time, I've always had my relationships, I've always had my friends, and I swear, the fame and all that, has not made me any happier."The secret of life is a decent relationship, making a difference ... and working for a living. That's it. Everything else is a bonus, and trivial.""