A long time ago there were pirates
Beaming waves from the sea
But now all the stations are silenced
'Cause they ain't got a government license
—"Capitol Radio," the Clash

PIRATE RADIO COULDN'T HAVE A BETTER OPENING SEQUENCE — or a better opening song. A preteen British boy heads upstairs in a house (and a country) that is clearly a tomb. His cadaverous parents wish him good night, but the boy is not going to sleep. He slips a transistor radio under his pillow, and listens as a "Radio Rock" DJ cues "All Day and All of the Night," one of the Kinks's explosive early bashers. The song's immaculately mid-'60s opening words? "I am not content...."

Writer-director Richard Curtis's wildly fictionalized account of the offshore radio stations that undercut the BBC from 1964 to 1968, Pirate Radio includes many sequences as seditiously exuberant as that one. Indeed, the high points are so delightful that it almost doesn't matter that, about half the time, the movie stalls, stumbles, or reaches desperately for an embarrassed guffaw. (I lost track of the number of shots that featured someone sitting on a toilet.)

Curtis, who wrote Four Weddings and a Funeral and turned to directing his scripts with Love, Actually, has made trademarks of overlapping stories and ensemble casts. His tricks include sudden shifts in tone and scatter-shot narrative, so that sad parts contrast happy ones, and sharp plotlines speed past dull ones. He also relies on the Risky Business approach to romance: Although Four Weddings and a Funeral and Notting Hill may be remembered as charming and sensitive, they both depict true love as beginning with hasty, awkward, and even tawdry one-night stands.

That continues in Pirate Radio, a bad-boys movie set on a ship whose only female crew member is the lesbian cook. When women arrive — and they do — it's for one purpose only. The parade of groupies includes January Jones as Elenore, who pretends to love tubby Simon (Chris O'Dowd) but really wants smooth-talking peacock Gavin (Notting Hill co-star Rhys Ifans, sporting an impressively non-Welsh British accent). The other featured sexpot is teenage Marianne (Talulah Riley), invited on board by Radio Rock's boss, Quentin (coolly bewildered Bill Nighy, who played an aging rocker in Love, Actually). Her apparent purpose is to deflower the tale's obligatory male virgin, 18-year-old new arrival Carl (Tom Sturridge), who is torn between respectful courtship and that tawdry one-night stand. (If only he'd seen Curtis's other films, he'd know that the two almost always overlap.)

At Christmas time, the ship is visited by Carl's mother, middle-aged party girl Charlotte (Emma Thompson), who seems not have slowed down much. She's friends with many of Radio Rock's principals, and eventually reveals that one of them is a man she'd never previously identified to Carl: his father. Meanwhile in London, Thompson's ex, Kenneth Branagh, plays Radio Rock's government antagonist, the near-fascist Sir Alistair Dormandy. (He even has a Hitler mustache.) Like the villain in a cartoon series, Sir Alistair is regularly foiled and usually fuming. He must get his way in the end, though; Curtis doesn't distort the history to the point of pretending that offshore radio didn't end. (In fact, he shuts it down early, claiming the pirates vanished in 1967 when Radio Caroline, the best-known of the shipboard broadcasters, lasted till 1968.)

Released months ago in Britain as The Boat That Rocked, Pirate Radio has been trimmed by 20 minutes as well as retitled. The movie got lousy reviews at home, and some claim the shorter version is better. (Others vehemently claim the opposite.) Purists were offended because the director plays loose with the facts and chronology. The story is set in 1966-67, yet Curtis includes songs from as late as 1971 (the Who's "Won't Get Fooled Again"). The director also pits Radio Rock against reactionary Tories, when in fact the pirates were crushed by a Labor government. (One reason for the hostility: The pirates brought advertisements to Britain's chastely non-commercial air.)

The film's standards of decency are decidedly contemporary. Token American DJ the Count (Philip Seymour Hoffman on a well-earned vacation from Amerindie movie misery) "drops the f-bomb" on the air, and Gavin cooingly tells the station's teen-girl listeners (who giggle and swoon in quick reaction shots) that he's "looking right up your skirts." Either of those lines of patter would have ended Sir Alistair's dithering about how to sink offshore radio; he would have prosecuted them for obscenity — and, to judge from what happened to U.K. hippie mag Oz, would have won. (By the way, Oz's saga is the subject of an upcoming movie, Hippie Hippie Shake, starring Cillian Murphy.)

The most significant deviation from history is that "rock radio" didn't actually exist in Britain (or the U.S.) in 1966; there was only Top 40, playing Frank Sinatra and Tom Jones as well the Stones, the Who, and the Kinks. (The movie does make room for a handful of non-rockers, notably Herb Alpert and Skeeter Davis.)

But Pirate Radio isn't a documentary, or even a romantic comedy. It's primarily a musical, especially in its zippier second half. Some reviewers have complained about the obviousness of using Leonard Cohen's "So Long Marianne" as the theme for Carl's possible lover, but they must have missed the rest of the movie's playful cues: The ship's DJs sing along with the Turtles's "Elenore" when that character is on board, and Cat Stevens's "Father and Son" plays as Carl tries to save his dad (who's now been identified) while Radio Rock founders in a sequence that uproariously parodies both Titanic and the British Army's rescue from Dunkirk.

When the ship goes down, the risk is not to the working-class passengers in steerage; it's to the station's record library. In mock-tragic inserts timed to the Who's flourishes, individual albums float by, the music of a generation about to be claimed by the cruel sea. It helps to know the discs to get the jokes, which is one reason that the movie's gotten indifferent U.S. notices. (One review — in Rolling Stone, no less — claims the film includes the Beatles and David Bowie, neither of which are heard.) One of the movie's funniest lines refers to an LP that many viewers won't recognize. I won't reveal the gag, but the album is the Incredible String Band's The 5,000 Spirits, or the Layers on the Onion.

Curtis may not know much more about rock than mainstream American movie reviewers. In one speech whose discographical slip doesn't seem to be ironic, he has Quentin attribute Mickey and Sylvia's "Love Is Strange" to the Everly Brothers." But its use of '60s songs is what distinguishes the film from being just another of Curtis's have-it-both-ways sex comedies. And the music's range, from "Dancing in the Streets" and "Wouldn't It Be Nice" to "My Generation" and "Street Fighting Man," is even broader than the movie's clutter of characters. That's one thing that Pirate Radio gets right: It evokes a moment when pop music was not content, even with itself.

PIRATE RADIO — 2009, 115 min; at Landmark E Street and Bethesda Row, and AMC Loews Cineplex Shirlington.