Nick Park on Shaun the Sheep's big screen debut: "It’s like 24. With sheep."

Already a children’s hero of the small screen, tablets and phones, here he comes with a full-length feature (in cinemas from 6 February). His agent must be brilliant: his name is in the title.

Shaun first appeared, fully formed, in the third Wallace & Gromit film, A Close Shave (1995). On screen for less time than it takes to cook a lamb chop, Shaun somehow became at least as famous as his more established co-stars. At the Bristol studios of Aardman Features, where Shaun’s movie debut is being created, I’m being treated to a behind the scenes tour, to see for myself how a six-minute cameo role is being spun into an all-new all-wool film.

When I arrive, the film is about half finished, which in animation terms means it’s already taken ages and there’s loads more to go. Tails are up this particular day at Aardman – and not just the woolly ones. The film-makers have just learned that Shaun has been voted by Radio Times readers as the most popular BBC children’s character of the past seven decades.

Shaun is so thrilled he can’t talk, and Nick Park, the man who created Wallace & Gromit, is equally pleased: “Bob Baker and I worked together on The Wrong Trousers and we decided to write another one. We thought of this story about sheep rustling and the wool trade, and came up with Shaun the Sheep. He was like an innocent victim, really, that became a hero.”

Nick says it happened at a time when studio work was scarce. “One film had fallen through and we were having a bit of a difficult patch and it was: how can we come up with some ideas to keep people working? I put a couple of ideas on the table and one was: what if Shaun had his own series? It was very sketchy but Golly really took the sheep and created all the characters around him – his own little world, separate to Wallace & Gromit. He ran with it, really – for four series.” (Golly is the nickname of Richard Starzak, who co-directs the film with Mark Burton and made such a success of the TV shows.)

Shaun also has Baby Spice to thank for his stardom. Nick says things skyrocketed when Emma Bunton appeared in a photo wearing a Shaun the Sheep rucksack. “His merchandise was already catching on. I think it’s something to do with his cuteness, heroism and cheekiness.”

The Aardman folk imagine that if Shaun were a child, he’d probably be between eight and 12 years old: “the kind of kid who – if he sees a big red button saying Do Not Press – he’s going to press it,” says producer Paul Kewley.