A British mockumentary about three couples competing in a contest for the most unusual wedding, written (like Christopher Guest’s superior examples) via improvisation, “Confetti” generates some mild chuckles but not many big laughs, and pretty much falls apart in its extended finale. And when it interjects drama and poignance into the mix, one’s likely to wince.

The premise, elaborated with lots of direct-to-the-camera explanations and ersatz “caught on the fly” footage, is that Confetti magazine, which specializes in marital material, conducts a competition among three engaged couples to put on the most original ceremony with the assistance of wedding planners Archie (Vincent Franklin) and Gregory (Jason Watkins). The couples selected by the editor (Jimmy Carr) are Matt and Sam (Martin Freeman and Jessica Stevenson), who plan a production based on old Hollywood musicals despite the fact that she’s quite tone-deaf; Josef and Isabelle (Stephen Mangan and Meredith MacNeil), court enthusiasts who plan one with a tennis motif; and “naturalists” Michael and Joanna (Robert Webb and Olivia Colman), who plan to marry in the buff.

Needless to say, there are complications. The sweet, nebbishy Matt and Sam are beleaguered by the interference of her pushy mother (Alison Steadman) and “choreographer” sister (Sarah Hadland) and his musician best-man (Mark Wootton), as well as the eventual appearance of her long-absent father (Ron Cook). Josef, a control freak with a short fuse, is insanely jealous of his wife-to-be’s Spanish coach and furious over any perceived slight, while Isabelle is informed that she needs a nose job if they’re to have any chance of winning. And Michael and Joanna rebel when they’re told they’ll have to put some clothes on so the ceremony can be photographed for the magazine spread. The ever-helpful Archie and Gregory try to smooth out all the ruffles, but with very limited success.

Still the contest goes on, and the three ceremonies take place, all of them elaborate theatrical productions. Though “Confetti” has had its problems up to this point–the entire Josef-Isabelle thread is too nasty to fit comfortably into the mix, the Michael-Joanna one is based on a premise that’s weak from the very beginning, and Steadman and Hadland are so shrill that they curdle the Matt-Sam section–the picture has generated some amusing moments and possessed a mangy sort of charm. But the weddings themselves are just too big, slick and fault-free–an absurdity when it’s shown that up till the very last moment each of them is in absolute turmoil. They’d be funnier–and more real–if they were smaller-scaled and less than letter-perfect–in short, if they looked as though they might actually have happened. And the obligatory postscripts are pretty limp.

The cast is variable, though all have their moments. But though the three couples are put at center stage, it’s probably the team of Franklin and Watkins that will prove the biggest crowd-pleasers. Their obvious affection for one another and determination to help their incessantly troubled clients maintain an oasis of near-stability amidst the surrounding madness. It’s also especially enjoyable when Cook, whom you might remember as Rowan Atkinson’s dense assistant in “Blackadder,” shows up.

There’s nothing technically remarkable about “Confetti,” which lays on the rough edges a bit too thick for comfort. And the stream of oldies on the soundtrack becomes rather less golden as the movie progresses. That’s, unfortunately, characteristic of the entire picture. It’s moderately amusing, but rather wan when compared to really inspired mockumentaries like Guest’s.