Sir Sidney Ruff-Diamond (Sid James) is Queen Victoria's Governor in the British India province of Khalabar near the Khyber Pass. The province is defended by the feared 3rd Foot and Mouth Regiment (The Devils in Skirts), who are said to not wear anything under their kilts. When Private Widdle (Charles Hawtrey) is found wearing underpants after an encounter with the warlord Bungdit Din (Bernard Bresslaw), chief of the warlike Burpa tribe, the Khasi of Khalabar (Kenneth Williams) plans to use this information to incite an anti-British rebellion. He aims to dispel the "tough" image of the Devils in Skirts by revealing that contrary to popular belief, they do indeed wear underpants under their kilts.
A diplomatic operation ensues on the part of the British, who fail spectacularly to prove that the incident was an aberration. The Governor's wife (Joan Sims), in the hope of luring the Khasi into bed with her, takes a photograph of an inspection in which many of the soldiers present are found wearing underpants, and takes it to him. With this hard evidence in hand, the Khasi would be able to muster a ferocious Afghan invasion force, storm the Khyber Pass and reclaim India from British rule; but Lady Ruff-Diamond insists that he sleep with her before she parts with the photograph. He delays on account of her unattractiveness, eventually taking her away with him to Bungdit Din's palace.
Meanwhile, the Khasi's daughter, Princess Jelhi (Angela Douglas), reveals to the British Captain Keene (Roy Castle), with whom she has fallen in love, that the Governor's wife has eloped, and a team is dispatched to return her and the photo to British hands. Disguised as Afghan generals, the interlopers are brought into the palace and, at the Khasi's suggestion, are introduced to Bungdit Din's sultry concubines. Whilst enjoying the women in the harem, they are unmasked amid a farcical orgy scene, imprisoned, and scheduled to be executed at sunset along with the Governor's wife. The Khasi's daughter aids their escape in disguise as dancing girls, but during the entertaining of the Afghan generals, the Khasi, contemptuous of an annoying fakir's performance, demands that he see the dancing girls instead. After their disguises are seen through, the British and the Princess flee, but Lady Ruff-Diamond drops the photograph on leaving the palace through the gardens. The group returns to the Khyber Pass to find its guards massacred and their weapons comically mutilated, in a rare moment of (albeit tainted) poignancy. All attempts to hold off the advancing hordes fail miserably, and a hasty retreat is beaten to the Residency.
The Governor, meanwhile, has been entertaining, in numerical order, the Khasi's fifty-one wives, each one of them wishing to "right the wrong" that his own wife and the Khasi himself have supposedly committed against him (though no such wrong took place). After a browbeating from his wife, Sir Sidney calls a crisis meeting regarding the invasion, in which he resolves to "do nothing". A black tie dinner is arranged for that evening.
Dinner takes place during a prolonged penultimate scene, with contrapuntal snippets of the Khasi's army demolishing the Residency's exterior, and the officers and ladies ignoring the devastation as they dine. Shells shaking the building and plaster falling into the soup do not interrupt dinner, even when the fakir's severed - but still talking - head is served, courtesy of the Khasi. Only Brother Belcher fails to display a stiff upper lip, and panics like a normal person. Finally, at Captain Keene's suggestion, the gentlemen walk outside to be greeted by a bloody battle being waged in the courtyard. Still dressed in black tie, Sir Sidney orders the Regiment to form a line and lift their kilts, this time exposing their (implied) lack of underwear. The invading army is terrified, and retreats at once. The gentlemen walk back inside to resume dinner, whilst Brother Belcher acknowledges the defaced British flag flying.
- Sid James ... Sir Sidney Ruff-Diamond (as Sidney James)
- Kenneth Williams ... The Khasi of Kalabar
- Charles Hawtrey ... Pte. James Widdle
- Roy Castle ... Capt. Keene
- Joan Sims ... Lady Ruff-Diamond
- Bernard Bresslaw ... Bungdit Din
- Peter Butterworth ... Brother Belcher
- Terry Scott ... Sgt. Major Macnutt
- Angela Douglas ... Princess Jelhi
- Cardew Robinson ... The Fakir
- Julian Holloway ... Major Shorthouse
- Peter Gilmore ... Private Ginger Hale
- Leon Thau ... Stinghi
- Wanda Ventham ... Khasi's First Wife
- Alexandra Dane ... Busti
- Michael Mellinger ... Chindi
- Dominique Don ... MacNutt's Lure
- Derek Sydney ... Major Domo
- Steven Scott ... Burpa guard
- David Spenser ... Bungdit Din's servant
- Patrick Allen ... Narrator (voice) (uncredited)
- Josephine Blain ... Hospitality Girl (uncredited)
- Johnny Briggs ... Sporran Soldier (uncredited)
- Simon Cain ... Bagpipes Soldier (uncredited)
- June Cooper ... Hospitality Girl (uncredited)
- Carmen Dene ... Hospitality Girl (uncredited)
- Anthony Dutton ... Burpa (uncredited)
- Eve Eden ... Khasi's Wife (uncredited)
- Barbara Evans ... Khasi's Wife (uncredited)
- Harry Fielder ... Burpa (uncredited)
- Liz Gold ... Khasi's Wife (uncredited)
- Angela Grant ... Hospitality Girl (uncredited)
- John Hallam ... Burpa on Rooftop (uncredited)
- Katherina Holden ... Khasi's Wife (uncredited)
- Nigel Kingsley ... Indian Boy (uncredited)
- Valerie Leon ... Hospitality Girl (uncredited)
- Tamsin MacDonald ... Khasi's Wife (uncredited)
- Vicki Murden ... Hospitality Girl (uncredited)
- Lisa Noble ... Khasi's Wife (uncredited)
- Anne Scott ... Khasi's Wife (uncredited)
- Larry Taylor ... Burpa at Door-Grid (uncredited)
- Sue Vaughan ... Hospitality Girl (uncredited)
- Patrick Westwood ... Burpa in Crowd (uncredited)
- Vicki Woolf ... Khasi's Wife (uncredited)
- Karen Young ... Hospitality Girl (uncredited)
- Casting by Weston Drury Jr - (uncredited)
- Art Direction by Alex Vetchinsky - (as Vetchinsky)
- Costume Design by Emma Selby-Walker
- Hairdresser - Stella Rivers
- Makeup Artist - Geoffrey Rodway
- Production Manager Jack Swinburne
- Assistant Director Peter Weingreen
- Second Assistant Director Ivor Powell - (uncredited)
- Props John Chisholm (uncredited)
- Set Dresser Freda Pearson (uncredited)
- Assistant Art Director Richard Rambaut (uncredited)
- Ken Barker Sound Recordist
- R.T. Macphee Sound Recordist (as R. MacPhee)
- Colin Miller Dubbing Editor
- Nicolas Le Messurier Sound assistant (uncredited)
- Charlie McFadden boom operator (uncredited)
- Otto Snel sound re-recording mixer (uncredited)
Camera and Electrical Department
- James Bawden camera operator
- Neil Binney camera operator: Khyber location
- H.A.R. Thomson director of photography: Khyber location
- Keith Blake clapper loader (uncredited)
- Steve Claydon focus puller (uncredited)
- Harry Gillard still photographer (uncredited)
Costume and Wardrobe Department
- Dorothy Edwards wardrobe supervisor (uncredited)
- Jack Gardner assistant editor (uncredited)
- Eric Rogers conductor
- Larry title sketches
- Yvonne Richards continuity
- Gladys Goldsmith continuity (uncredited)
- Julie Mendez choreographer (uncredited)
- Second film in the series with an alternative title.
- The Rank Organisation's 'title consultants' wanted to call this film 'Carry on the Regiment'.
- When Princess Margaret visited the set during filming, she was shown a clip which includes the scene in which Sir Sidney Ruff-Diamond writes to Queen Victoria, in which Sir Sidney says "Dear Vicky". Princess Margaret was said to be furious about this joke.
- First and only "Carry On..." film for Roy Castle. He replaced Jim Dale, who was unavailable.
- Tommy Cooper was originally asked to play the role of the Fakir but he was unavailable. Cardew Robinson was then cast in the role.
- The censor had a problem with Bungdit Din's line, "Fakir, off!" A sufficient pause was required between the words "Fakir" and "off".
- When the first Gulf War started, this film was banned from being shown on British television.
- In the dinner scene, the cast was served ham and boiled potatoes.
- There is an in-joke to the Rank Organisation: when someone bangs a gong (the trademark symbol of Rank), the Khasi describes it as "rank stupidity".
- Snowdonia in Wales doubled as the Khyber Pass with the rest of filming done at Pinewood Studios. When the film was released, an old soldier who had served in the Khyber Pass area wrote to the film studio, informing them that he recognized the area at once.
- Lady Ruff Diamond's line, "Oh dear! I seem to have got a little plastered," was an ad lib by Joan Sims which was kept in. Julian Holloway's (Major Shorthouse) reaction to the line was genuine.
- Joan Sims wore a body stocking during the dance scene due to her own concerns about her weight.
- Joan Sims complained to the Director Gerald Thomas about Kenneth Williams's behaviour while filming a love scene. Williams broke wind violently during the scene, which took Sims completely by surprise.
- To receive an 'A' (PG) cinema certificate some risqué dialogue was removed including Brother Belcher's request for "A tool to dig with" and Bungdit Din mentioning a "travelling fakir". The print remains edited to this day.