The benefit of 30 years of hindsight – and especially having been a little kid in love with all things Muppets at the time – reveals how deceptively cheap and small-scale this film is.

There's an indistinct villain with indistinct motives in Charles Durning's restaurateur, an almost conflict-free narrative device as the gang meet up and cross country to make it in Hollywood, and almost no barrier to their success once they get there (Orson Welles' booming baritone telling his secretary to draw up the standard 'rich and famous' contract).

But it's a charming and sweet origin story to the Muppet mythology that was never explored in the TV show. Kermit the Frog is living a simple life in his swap when a harried showbiz agent (Dom Deluise) comes along in a row boat desperate to find safety, off-handedly telling Kermit he should go to Hollywood and try and become a movie star.

Unable to shake the idea, Kermit decides to give it a try, meeting everybody who'll form the erstwhile Muppet family along the way. Fozzie's performing unappreciated comedy in the closest thing a Muppet film would have to a seedy strip club, Rowlf's a hotel pianist, Gonzo's a plumber, Dr Teeth and the Electric Mayhem Band are playing a disused rural church, Dr Bunsen and Beeker have a lab set up in an old Western ghost town and the current beauty Queen of Bogen county is the glamourous Miss Piggy, whose fate is sealed when her eyes meet Kermit's across a fairground.

They all reach Hollywood amid a flurry of 70s era star cameos and lay down a template that was revisited so successfully in 2011's The Muppets. If you loved the show as a kid you can't call yourself a fan until you've seen this movie.