Mr. Pilkington (Peter Gawthorne) is one of the top executives at the British Broadcasting Corporation, and today he is being driven into work at Broadcasting House while he reads over his notes and letters. Once he arrives and steps out of the car, however, he is in for a shock as a pair of combinations lands on his head; outraged, he looks up to see where the underwear has come from and notices that someone has hung their washing on a line between two of the building's transmission masts. On further investigation, there are two stowaways living on the roof...
This is purportedly the story of how the groundbreaking BBC radio series Band Waggon got its start, a series which made stars of Arthur Askey and Richard Murdoch, here billed as "Stinker", his nickname at the time (although he's probably better known to a younger generation as the English language narrator of The Moomins on television). While in the seventies it was customary to adapt TV comedy, usually sitcoms, to the British cinema, back in the forties it was radio that filmmakers drew their comic inspiration from, as the natural successors to the music hall where the likes of Askey would have started out.
Band Waggon actually came to an end around the time the film was released, but the novelty of seeing the public's favourite radio series on the big screen was not to be underestimated, and as there was a war on many of these operated as propaganda too. Hence the inclusion of a half-hearted Nazi-bashing subplot when "Big-Hearted" Arthur and "Stinker" Murdoch end up in the countryside. They are banished there because they have been chucked out of the roof-based retreat they set up on the BBC while waiting in vain for an audition, but stuffy Mr Pilkington hates dance bands and modern entertainers, so their chances were slim anyway.
Appearing at the Beeb gives the film an opportunity to have some of their stars appear in cameos for bits of business with the stars, allowing audiences to see what that radio gardening expert looked like or whatever, but the main narrative for this is more concerned with setting up a rival to the state broadcaster. No, Arthur doesn't end up interrupting the news to claim to be a representative of Ashtar Galactic Command, but he does use the television equipment he finds in the country house he has acquired to set up a pirate broadcast of Band Waggon, complete with a Jack Hylton's dance band who handily have been playing nearby.
Why are there cameras and the like in this old house? Because the Nazis have left them there, planning to return to send transmissions to Germany. They have a British stooge in the person of Jasper (Will Hay's old sidekick Moore Marriott) who scares people away from the mansion by dressing up as a ghost. After frightening Arthur and Stinker away when they try to stay the night, he has a change of heart when he finds out who his masters are and the stage is set for Britain to see the first competition to the BBC. All this and an exploding goat as well, along with the world's longest rendition of "Hands, Knees, and Boomps-a-Daisy" which takes up most of the climax of the film: nobody is claiming this to be an eternal classic, but its silliness is harmless and despite low expectations it does generate a few laughs.