The TV-derived summertime special has again become a fixture of the British film industry, as it was in the heyday of Please Sir! The Bad Education Movie, an end-of-term runout for Jack Whitehall’s delinquent teacher Alfie Wickers, opens in roughly the same slot in which The Inbetweeners and Mrs Brown’s Boys spin-offs profited in previous years. The numbers on those films amply bear out the rationale that putting any cheap tat in enough cinemas will turn a tidy profit; here, then, is one last jolly for Class K before they collect their exam results, and Whitehall becomes a blip on the Hollywood radar.

The school’s-out vibe generates a truly obnoxious first half-hour: you sense Whitehall and co-writer Freddy Syborn egging one another on to see who can scrape the bottom of the barrel quickest and loudest. Mushrooms are unknowingly consumed at an Anne Frank exhibition. The school hamster bounces into Joanna Scanlan’s nethers. Wickers ingests a foreskin kept as a holy relic. Yes, it’s laser-guided at the same gurgling demographic that would willingly endure a Snog, Marry, Avoid marathon. But even teenage boys might find the desperation to shock a boner-killer: the film’s initial comic touch makes Seth MacFarlane seem like Ernst Lubitsch.

With this opening barrage out of its system, Bad settles into its true rhythm; instead of egregiously bad jokes, we get potentially good ones indifferently told. For starters, it’s sort of funny that austerity measures mean this filmic subspecies must now travel to Cornwall, rather than the exotic Costa Plonka. Series director Elliot Hegarty has modest fun within a pub serving as a Cornish Liberation Army stronghold, where the ladies’ loo is a door painted on a wall, and we get a Little Britain-ish doodle of the Cornish gay scene: one middle-aged bloke called Colin, who attempted to order a spritzer in 1984.

Even here, though, there’s uncertainty as to whom the joke’s really on, and events descend into the kind of clumsy farce (knives in hands, people on fire) that suggests nobody present really had much idea how to build a scene. It is, likewise, a workable idea to have Wickers and his charges mistaken for a terrorist sleeper cell, but having larded the soundtrack with Grimshaw-friendly grime, Hegarty hasn’t the resources left to play it out: instead we’re given cop Clarke Peters looking concerned in a school hall, and a last-reel runaround in a heritage centre that yields hot-button references to Cheryl Cole and Braveheart.

Here, at least, the film permits us some fresh air. Elsewhere, laughs are stifled by Hegarty’s TV aesthetic, all static medium and closeup shots, chiefly of Whitehall’s ever-harassed testes. Stretched this high and wide, the star’s posh-boy persona can rarely have seemed so charmless; the film acknowledges as much in nudging on Jeremy Irvine as a braying toff whose sole purpose is to make the goon-like Wickers appear admirable.