Yet it's here where the magic happens. "Performance is the thing we love here," Lord says, when he ushers me into a screening room to watch clips from the . Behind him is a picture of Shaun, sitting by a pool, reading a screenplay, with "The Birds" crossed out and replaced by the title "The Sheeps".

It is, of course, another Aardman gag. "There's not a lot of Hitchcock in there," Burton tells me, although film influences are still strong and feature everything from Jacques Tati movies to .

has been made quite quickly, taking about four years; Aardman usually devotes five years to a feature-length project. Originally scheduled for a March 2015 release, the movie had its world premiere at the Sundance Film Festival on January 2 and its Hong Kong opening is timed for the first day of the Lunar New Year of the Goat (or Sheep - since there's no linguistic differentiation in Chinese among the two).

Nicknamed "Golly" (his original surname is Goleszowski), Burton's co-director Richard Starzak's association with Aardman stretches back years. His credits include Peter Gabriel's landmark music video, which was made using stop-motion; the painstaking 3D animation technique that has been the company's mainstay for years. Shaun is largely his baby.

"I've been working on for about 10 years," he says. So does Starzak still observe real-life sheep behaviour? "I'm past that. When we started devising Shaun, I took a walk in the countryside, and all these sheep came to the gate, staring. I realised how different they were. They started bleating - some were baritones, and there were lots of different pitches within that. When they bleated, it was like they were telling a joke."

Shaun the Sheep first featured as a character in Nick Park's 1995 Oscar-winning short , alongside the famed man and his dog, Wallace and Gromit. Eventually it was decided that Shaun would get his own television show and Starzak came on board, although he was nonplussed by the early ideas. "I didn't like what was going on. Shaun was at the top of the tree; he was a cool sheep, with sunglasses and a bike and a cash card, and he used internet cafes. It didn't feel very Aardman."

Starzak wanted to steer the show towards something more like - the Aardman-produced shorts that won Park his first Oscar at the 1991 Academy Awards. That had talking animals, but they wanted this to be different. "We wanted something more plausible, more real," Starzak says. "A sheep's job is to eat grass."

Sheep don't talk, so a style akin to silent comedy was born. Even the hapless, myopic farmer, who oversees Shaun's farm, speaks in a mumble.

Arriving in 2007, the show has unfolded more than 130 episodes. But creating five-minute episodes, usually based around a gag or two, is very different to creating a feature-length film. "You have to try and find a story that can sustain 80 minutes," says Burton. "You have to give your characters emotional lives. They have to get out. We like to use this phrase 'learn something', but they need to get out and have an experience, and change a little. We put our characters through the wringer."

The film will be recognisable to those who've watched the television series, which has aired in 180 countries. Living at Mossy Bottom Farm, Shaun will be joined once again by the Flock, his less intelligent siblings, the Farmer and his loyal sheepdog Bitzer. When the Farmer develops amnesia and wanders around the city in a haze, the characters leave the farm for the first time. There are a few new characters in the movie - notably Trumper, an animal containment officer, who spends his days capturing stray creatures and locking them away.

The movie's story has been a process of evolution, say the directors. At one point, there was a plot involving a wolf (presumably in sheep's clothing); another early idea had the villainous Trumper as a farm inspector, an idea that kept the story in the countryside. Remarkably, the day before we meet, after a test screening in London, the team came up with a new ending. "You're always fine-tuning," says Burton. "You just keep on twiddling until they tear it out of your hands."

Part-way through the conversation, Lord joins us for lunch. "Any food left?" he says, popping his head round the door and helping himself to a plate of sandwiches. Credited as a producer on the film, Lord is there to cast an objective glance over the project. If anything, he and Sproxton have set the tone for Aardman's philosophy over the years. "It's all for a very broad audience," he says. "Nobody thinks 'We'll put that joke in for the kids'."

Culture-wise, there seems something quintessentially British about Aardman. "We're a similar age-group influenced by the same things I suppose, whether it's films or [children's comic] - things that made me laugh as a kid," says Starzak.

Yet the references aren't all nostalgic. One set I visit of a cityscape shows a billboard of the Farmer, who becomes a celebrity hairstylist after his memory loss, pictured with two pairs of shears. He looks a lot like Hugh Jackman's character Wolverine.

Visiting an Aardman production is a sheer (no pun intended) wonder. There are many "hot" sets being filmed at any one time, with multiple animators working on various shots. I'm introduced to Steve Cox, who has been patiently putting together a shot set around a graffiti-strewn underpass, where the Flock are passing sticks to each other, chain-gang style. He started yesterday, shooting the models a frame at a time (24 frames equals one second of screen time).

Burton and Starzak's job is to keep tabs on their animators, before assembling the footage. "Our time is not our own," laughs Starzak. "We've both got an assistant director - and they're always there. Even when you go to the toilet, you can hear them outside. You're infantilised a bit, led from set to set."

Understandably, both men can't stop thinking about sheep. Starzak has recently moved to a house in the countryside and the first thing he hears when he wakes up is bleating. Burton, meanwhile, admits that he had been counting Shauns to get to sleep every night. "I've done that a lot - I do a lot of Shaun the Sheep dreaming."

If it was not already obvious, "I am fond of sheep," Starzak says with a laugh.

Burton nods in agreement. "They are comic, aren't they? They are absurd. You could argue we humans are as well, but there is something absurd about sheep as a species."