Clocking in at 80 minutes, the two-episode season finale of “Extras” (“Extras: The Extra Special Series Finale”), which will air Sunday on HBO, comes close to being a standalone movie. It’s also a Christmas movie of sorts, with sentimental passages, a fleeting biblical reference or two (“No room at the inn…”), marquee names (Clive Owen, George Michael, Gordon Ramsay), and a self-loathing narcissist as its hero who gains a sneak peek at redemption at the end.

The latter would of course be Andy Millman, the frustrated extra turned sitcom star played by the British comedian Ricky Gervais. Together with his writing partner and fellow performer Stephen Merchant (who appears as Andy’s toweringly incompetent agent, Darren Lamb), Mr. Gervais was the original creator of “The Office,” the hit BBC comedy that spawned the successful NBC remake and imitations around the world before closing shop after just two seasons.

Mr. Gervais is said to enjoy hanging around the set of the American “Office,” and has even written an episode for it, so it might appear surprising that, as with his first series, he and Mr. Merchant have apparently decided to take an ax to their follow-up show after a mere two seasons. But this points to the double-edged moral of their “Extras” finale. That it has a moral — that it even dares to be didactic — is appropriate given the Christmas-tinged subject matter. The overt moral is that Christmas is no longer the “season of giving” (early on we are shown a pair of particularly hideous toys) so much as the season of renunciation, at least for the fame-obsessed Andy, whose low-brow fictional sitcom, “When the Whistle Blows,” leaves him perpetually dissatisfied no matter how many of his countrymen tune in to watch, and despite the fact that it has landed him a massive apartment and a regular seat at the see-and-be-seen showbiz restaurant, the Ivy.

The “inside” moral, appropriate in that “Extras,” like “The Larry Sanders Show” or “Curb Your Enthusiasm,” is about the entertainment industry, is a rejection of the idea that a television series should be kept going as long as possible if the ratings hold up. In this, Messrs. Gervais and Merchant are following in the footsteps of John Cleese, who called a halt to “Fawlty Towers” after a mere 12 episodes, feeling that anything more would be redundant.

Although there are plenty of British series that go on forever, along with network chairmen who are determined they should do so, pulling the plug on a show before you have to is, needless to say, a very un-American attitude. Rather than farm out episodes to other writers, the authors have preferred to keep an iron grip on their creation and end it on their own terms.

“Extras: The Extra Special Series Finale” begins with Andy appearing on “Celebrity Big Brother,” in which a cast of wannabes and has-beens have to perform such demeaning tasks as ranking themselves in terms of name recognition. The electronic bleeps that usually block out the plentiful swearing are replaced (in a wonderfully surreal and comic touch) by birdsong.

Having rapidly established that Andy is in the entertainment world’s version of hell (“The Victorian freak show never went away, only now it’s called ‘Big Brother’ or ‘American Idol,'” he complains), we backtrack six months to when he is still the star of “When the Whistle Blows.” Darren is still his agent, the sweet but incurably dim Maggie (Ashley Jensen) remains his only real friend (though Andy treats her with increasing cruelty), and the glamorous film roles he craves still elude him.

Could the fault lie with Darren? A chance encounter with a slick agent, Tre Cooper (Adam James), persuades Andy that the rarefied blend of fame and artistic integrity he craves is attainable — so long as he fires Darren, which he promptly does by leaving a phone message. Darren finds out about this from his only other client, Barry (Shaun Williamson), who hangs around the office and performs such tasks as helping Darren remove his anorak by pulling it over his head because the zipper’s broken. With Andy gone, they close the office and get jobs at a car phone store.

Seduced by Tre’s flattery, Andy is soon convinced that real stardom awaits. This leads him to make some very foolish decisions that I won’t disclose here. And while the send-ups of guest stars such as Clive Owen — for which “Extras” is famous — prove (as usual) too exaggerated to be plausible, Mr. Gervais’s poison-pen portrait of his own character as an envious, bitter publicity hound is a thoroughly convincing rendition of the pursuit of fame for its own sake. (“Be careful, mate,” Barry warns him after he’s left Darren. “Fame is a mask that eats into the face.”) Mr. Gervais’s satire is also much sharper when it’s about famous people who aren’t his guest stars. “Look at that,” he says to Maggie over lunch at the Ivy. “Harold Pinter and his wife having lunch with [former Spice Girl] Geri Halliwell. Why am I not having lunch over there?”

“I’m sorry you’re stuck at this table then,” she replies tartly.

If the finale of “Extras” counts as a Christmas film in more than a seasonal sense, it’s thanks to its emphasis on loneliness and poverty (after losing her job as an extra, Maggie is reduced to cleaning toilets and moves to a god-awful bedsit), the callousness of those who have it all (“Life’s cruel,” Tre is fond of saying with the satisfaction of someone who’s so far found it kind), and ostentatious “charity” as opposed to authentic generosity.

“So, what kind of charity work are you involved with?” asks a reporter for the Guardian who’s writing a profile of Andy that goes disastrously wrong. “Africa,” he replies with a shrug. “Main one people care about, isn’t it?”

Needless to say, Andy donates nothing to “Africa,” which is perhaps one of the better things you can say about him. He’s not calculating enough to be a true phony, though he is self-absorbed enough to be genuinely unpleasant.

Lest all this sound unremittingly grim, this is the time to say that this last episode of “Extras” is filled with wickedly uncomfortable comic scenes in the classic Gervais-Merchant manner. Mr. Gervais is a curiously joyless comedian — or perhaps more accurately, a comedian who takes modern joylessness as his subject — but he does reserve a touch of genuine joy for himself and Maggie as they ride off into the sunset. It’s funny, too, and Maggie, dear dumb faithful Maggie, not Mr. Gervais himself, is given the best lines, which I’m pretty sure is part of the point.

bbernhard@nysun.com