Since Hugh Grant quoted David Cassidy at a bemused Andi MacDowell in 1994, UK wedding comedies have become an institution to rival marriage itself. Aptly, in a week that’s seen marriage conventions on their way to a long-overdue update, along comes a film to shake up the rom-com in turn. Instead of watching Josh (Rafe Spall) and Nat (Rose Byrne) follow a twisty, misunderstanding and obstacle-strewn path to their eventual union, we’re there to witness their relationship fall apart. Moreover, we’re willing it to happen, like the snide friends and relatives behind the film’s titular prophesy. Josh and Nat don’t work as a couple, and Mazer’s film uses their incompatibility as the backdrop to a series of very funny, recognisable sketches about couples that don’t work. Luckily, Faris and Baker are naturally likeable on screen, while Byrne and Spall are enormous fun as the romantically divided leads. Spall has emerged from the cinematic side lines as a bona fide charmer, proving himself especially well-suited to awkward comedy in a posh lingerie shop scene and a couple of reputation-destroying encounters with Nat’s uptight family. Byrne too – who perhaps didn’t receive the attention she deserved next to Kristen Wiig and Melissa McCarthy for her excellent comic performance in Bridesmaids – is a real asset to the film, and more than capable of delivering a timely punch line. Some of the film’s funniest moments, it should be said, belong to the bit characters. Stephen Merchant is hugely enjoyable as Josh’s regrettable best friend, as are Tim Key and Olivia Colman as the solicitor who draws up the couple’s living will and their less-then-ideal marriage counsellor. It’s Nat’s caustic sister (Minnie Driver) who delivers the “I give it a year” dark-fairy-at-the-christening curse, and she too receives her share of nicely naughty lines. One or two of the film’s gags outstay their welcome, lingering to plump up the 97-minute runtime, but nothing grates. The litany of Josh and Nat’s relationship niggles is well observed stuff and sure to inspire more than a few knowing nods from the audience. On the promotional circuit for I Give It a Year, writer/director Mazer (Bruno, Borat, Ali G Indahouse) said he wasn’t aiming to pull at the heartstrings, making the film’s lack of romance less of a misfire. If he set out to invert a few generic conventions and tell some good gags along the way, then there’s no failure here. So what if the ‘rom’ is sacrificed for the sake of the ‘com’? If you have to choose, I know that’s the way around I’d have it. Follow our Twitter feed for faster news and bad jokes right here. And be our Facebook chum here.