Wet Weather Cover, King's Head Theatre

"Plays about cinema tend to be written by people who have done some movies, come back and filled their fountain pens from their spleen," the Oscar-nominated screenwriter Larry Gelbart once told me. David Mamet's Speed-the-Plow is probably the best-known example, followed by such works as Christopher Hampton's Tales From Hollywood, Martin Crimp's The Treatment and, most recently, last week's The Little Dog Barked. Oliver Cotton's diverting comedy (they are invariably comedies) sits very snugly in that long dyspeptic tradition, bringing few fresh insights to the party but lifted by some sharp writing and a trio of outsize, roaring-boy  performances that threaten constantly to split the seams of this compact venue. Tip: try not to sit in the front row.

The first thing you clap eyes upon on entering the theatre is Tanya McCallin's terrific set, the cross-section of an enormous caravan (supplied apparently, by Essex Caravan Breakers) which prompts pleasurable ship-in-bottle speculation on how it was shoehorned into the King's Head. The title refers to the "back-up plan" in a movie's shooting schedule when bad weather makes it impossible to film outside. Rain has stopped play for very many days indeed on the Spanish location of Cortez, a lamentable-sounding Hollywood epic about conquistadores, and the never-seen English director Derek is apparently fast running out of wet-weather ideas. Meanwhile its "stars", if such they can be called, circle each other irritably like mangy lions in their leaky, ramshackle cage while indecipherable crackles of white noise come in from the front on a walkie-talkie and a high-camp dresser who only speaks Spanish throughout (Pepe Balderrama), erupts at regular intervals with insults and changes of frilly shirt.

Basically, though, it's a duel. One of the resting actors, barnstormingly played by Michael Brandon, from Dempsey and Makepeace and Jerry Springer the Opera, is a brash, slightly vainglorious New Yorker. The other is a Brit, played by Steve Furst, who has the hangdog look of a limey Steve Buscemi. Their barbed exchanges and pissing contests (Who has the bigger billing? Which was the worse national tragedy, 9/11 or the Blitz?) also take in some rather obvious observations about the differences between British and American acting styles and, as they swap notes on Shakespeare and Marlowe, which they'd clearly both much rather be playing, the ineffable cheesiness of Hollywood studio productions.

Nothing very much new here, though Cotton, an actor whose first play this is, recently appeared in a poorly reviewed film about Pope Joan and so presumably knows whereof he speaks. And he has a definite knack for both one-liners and sustained comic setpieces - Brandon belting out John of Gaunt's speech from Richard II in a broad Bronx accent, or the two men improvising a fabulously improbable variant on one of Cortez's more lacklustre scenes.

He's also very good at nailing their shifting balance of power, as Furst's long-suffering sidekick gradually gains a subtle ascendancy over Brandon's Withnail-like braggart (there are shades of Bruce Robinson's cult film in the central set-up). A cracking pace is set by the director, Kate Fahy, another actor trying on a new hat for the first time. It's difficult to gauge the play's broader appeal from the enthusiastic laughter of insider recognition last night (when the audience seemed culled substantially from the acting community) but overall I'd hazard a guess that the forecast looks bright.

Wet Weather Cover continues at the King's Head Theatre, Islington until 21 February