The novelty of “The Belles of St. Trinian’s” might be the sight of Alastair Sim in a dress.

The cinema’s defining Ebeneezer Scrooge and a mainstay of postwar British comedies and dramas — he had the title role in the original “An Inspector Calls,” and Hitchcock hired him for “Stagefright” — he took on two roles, as siblings, in this 1954 farce.

But the life of the party here would be the inmates in this asylum, the brash, bedlam-inducing hellions of St. Trinian’s School for Young Ladies. They gamble, cheat, manufacture “bathtub gin,” cross and double-cross one another and leave mayhem in their wake. They’re the reason this comedy is so beloved it has warranted revivals and remakes in the UK over the decades.

It seems the stiff upper lip Brits couldn’t get enough of teen girls behaving badly in a “Stalag 17” styled school comedy.

The plot — a sultan (Eric Pohlmann) needs a place to park his youngest daughter, seeing as how he’s had to “allow the Americans to build their airbase” in his kingdom. Memories of GI mischief during WWII had not been forgotten by the British screenwriters.

St. Trinian’s is recommended, conveniently located near the stables where the sultan’s racehorses are boarded.

Little Fatima may not know what she’s in for, but the residents of town (Stanstead Abbotts, Hertfordshire) sound the fire alarm, board up their store fronts and flee when the train approaches to deliver the students for the fall term.

The local constable locks himself in his cell.

When the girls pelt out of the passenger cars, we see why. They’re unruly, uncontrollable and unstoppable. Miss Millicent (Sim) and her staff (Hermione Baddeley, Balbina, Joan Sims, Renee Houston and Betty Ann Davies among them) barely even try.

The school’s broke and in disrepair, but having a sultan’s daughter could get the staff and local vendors paid, if they play her “pocket money” right.

Millicent’s gambler-brother Clarence (Alastair Sim again) has his own designs. He’s re-enrolled his brassy, streetwise daughter (Vivienne Martin) so that she can befriend young Fatima (Lorna Henderson) and get the skinny on her daddy’s star stallion, Arab Boy, for the upcoming Gold Cup “hunting” (steeplechase) race.

With all the crime and graft and general misbehavior that has nothing to do with education going on, the police send a policewoman (Joyce Grenfell) undercover, taking a job as “sports” mistress, to catch all these miscreants in the act. Or acts.

Hey, when the school motto is “In flagrante delicto,” what would you expect?

The kids set booby traps and pull pranks.They run all manner of scams via their “go between,” the trenchcoated hustler Flash Harry (George Cole, hilarious) who was hired as a teen gardener’s assistant but “disappeared” into a life in in the hedges in 1940. Harry places bets, bottles and sells their chemistry class “bathtub gin” and is fixer for whatever schemes they cook up.

The field hockey team never loses at home, and not just because they play rough, disable the referee and jeer the opposing team without pity. The girls make their home end goal “two feet smaller” than their opponents. Try scoring in that.

There are cliques and factions, which become clearer when Clarence and his daughter Arabella conspire to get Arab Boy out of the Gold Cup, by hook or by crook.

That’s Arabella’s idea, by the way.

Other girls have money on Arab Boy to win. So it’s game on, with the hapless adults mostly bystanders in the shenanigans to come.

The film’s Cockney touches and the screeching underclass accents of the young ladies (one of the jokes) may move you to turn the closed captioning on.

You don’t want to miss throwaway lines like “Listen, rabble,” and “put the screws on the old custard” and hear the undercover policewoman described as a “copper’s kick, in skirts.”

It’s not “holly jolly pulse-throbbing” for the first hour, as the set-up is set up and we’re treated to single scene sight gags, like the booze and smoke filled teacher’s lounge (they don’t bother hiding this from the young “ladies”), the school inspectors who came and were corrupted and kept as a veritable harem of the French teacher (Balbina) and her salon.

It was a daring movie for its day, almost racy for its 1954 depiction of “young ladies” doing what needed to be done in still-“Broke Britannia.”

Director Frank Launder was better known as a screenwriter (Hitchcock’s “The Lady Vanishes”), but he put the very first “Blue Lagoon” on the screen in the 1940s, and made a cottage industry out of “St. Trinian’s” comedies as a director.

The third act here is why “The Belles of St. Trinian’s” is held in such regard, to this day. It’s a near riot of action, climaxing with a restaging of the “Zulu Wars” in the crowded halls of a tumbledown manor house turned boarding school for girls.

MPAA Rating: “Approved”

Cast: Alastair Sim, Joyce Grenfell, George Cole, Vivienne Martin, Hermione Baddeley and Eric Pohlmann

Credits: Directed by Frank Launder, script by Sidney Gilliat, Val Valentine and Frank Launder. A Film Movement release.

Running time: 1:31