I have eyes just like Gromit's. They're in the palm of my hand.

For the last hour, I've been trying to create a replica of the Wrong Trousers star's head as part of a behind-the-scenes tour of his creators' studio - Bristol's Aardman. I've rolled white clay into tiny spheres, pressed a miniscule blob of black into them so that a quizzical little eyeball stares back at me. Now, all I need to do is stick them on to the face I've sculpted (with the expert help of Aardman modeller Will Harding). I take hold of the miniature ball between my finger and thumb and ... promptly drop it on the floor.

It doesn't go down well.

"Losing eyeballs on a dark set," says Harding, shaking his head. It is, apparently, one of the more annoying habits of Aardman animators - the team who move around the models that Harding lovingly crafts. "They'll say 'oh, that's fine, we've got loads of spare ones' but they take ages to make." Indeed, the proper moulded plastic eyeballs used in Wallace & Gromit films are a little more advanced than my plasticine effort - they each come with a tiny hole in each pupil so that animators can move the eyeball around with intricate metal tools.

Such eyes have been in high demand at Aardman recently as the team put the finishing touches to the new Wallace & Gromit film - a franchise stretching back 34 years, since we first met the lovably obtuse inventor and the wise, super-capable canine who helps rescue his owner's disastrous schemes. Vengeance Most Fowl is their first television outing since 2008's A Matter of Loaf and Death, and their first feature-length film since 2005's Curse of the Were-Rabbit. Back then, director Nick Park said they'd never make another full length movie. It was too long. Too exhausting. And yet ...

"The plan was just to do another half an hour," says Park, who today is very on-brandly sipping coffee from a Gromit mug. "And then we started thinking of more ideas, like, oh, we could bring back Feathers McGraw! It kept growing bigger."

You can tell. Aardman's studios are a hive of productivity - down every corridor are little rooms in which people tinker away on replica canal boats or fiddle with tiny clay arms. I have to promise to be on my best behaviour. Apparently on one previous set visit a French journalist picked up a figure in a live scene meaning the whole thing had to be shot again from the start. "That was very upsetting," says my guide.

We start off in the puppet making workshop where Natalaya Hamideh shows me a variety of characters - including new addition PC Mukherjee. I hadn't realised that each model has a wire armature that sits inside them like a skeleton. Without it the characters would sag and bend whenever they were required to hold another object. Even PC Albert Mackintosh's moustache has a wire in it for when he needs to express emotions through facial hair alone.

The modellers have certainly been busy. There are multiple versions of Wallace and Gromit in sitting or standing positions, along with 60 versions of Norbot - a smart-gnome (voiced by Rhys Shearsmith) who the plot revolves around.

Vengeance Most Fowl's storyline chimes with our current anxieties around technology. Gromit feels pushed out when Norbot arrives on the scene to complete all of Wallace's odd jobs effortlessly. When the returning Feathers McGraw hacks into Norbot from the high security prison he's festering in, Norbot turns rogue, recruiting an army of fellow gnomes to build a submarine that can break Feathers out of jail.

Last year it was reported that Aardman had run out of modelling clay but the team say this was overstated: while there were supply issues it was never a serious problem. And yet the Aardman office had fans calling up to offer them clay from their garden. "One retired professor even said he could come up with a formula to make more," laughs producer Richard Beek. These days the modelling clay isn't as central as it once was - many models are made with silicone which gives them a steadier structure (to retain the homemade feel, fingerprints are added to the silicone moulds).

I'm whisked off to the art department, where "everything you see on screen that's not puppets" is made. For Vengeance Most Fowl that means a scenic waterway designed for a high speed canal chase and an impressively ramshackle submarine made out of stolen garden items: bath planters, rakes, drain pipes for periscopes and so on. Part of the challenge is not to make anything too snazzy. "It shouldn't distract from the characters," says Matt Perry, the film's production designer. When they first made the submarine it looked a little too fabulous for something supposedly compiled from garden detritus. So one member of the team got to work smacking dents into it, which alarmed passing visitors. "Weathering is also important," adds Perry. "The police station's desk has to have the right amount of rust for a desk of that era."

As with all Wallace & Gromit films, eagle-eyed viewers are rewarded with all kinds of smart references. The submarine is a nod to Nautilus, Captain Nemo's vehicle in Jules Verne's Twenty Thousand Leagues Under The Seas. Elsewhere, lead graphic artist Gavin Lines entertains himself with all sorts of gags that might only flash on the screen for a second or two (Gromit's record collection this time around contains Walkies on the Wildside). These days he follows strict rules - it has to be family friendly and it has to be legal. "I did get into trouble before," he admits. Whereas Smeg have apparently always seen the funny side of their fridges being rebranded as Smug, Bosch were less than happy about Gromit using a "Botch" tool in Curse of the Were-Rabbit. "We weren't allowed to use it on any promotional material," says a chastened Lines.

My next stop is at the director of photography's studio. Dave Alex Riddett has worked on every Aardman production since 1989's Grand Day Out. And despite the technological advances that allow them to do things much faster now, he says the whole team are really just striving to retain the feel of the early films. Riddett is currently filming some kind of lair for Feathers's evil gnome army which lights up "like the best disco you've ever been to ... we're trying to get it commissioned for the wrap party as well!"

Without missing a beat, it's time to meet the animators. If this tour is anything to go by, I understand why Aardman film projects run so smoothly - everyone is at their station at the right time to meet me and more than happy to explain their role as they work.

Sean Gregory's job is to move the characters a tiny fraction before the camera operators take a shot. Each movement is around a millimetre; any less, says Sean, and you can't really see what you're doing. He works largely on instinct. "You just lightly tap it the tiniest bit," he says.

I look around his dark studio and think about the fact that it takes each animator a whole week of working like this to capture just five seconds of film. Doesn't it send him loopy?

"It drives you mad sometimes," he admits. "Most of the time, actually. But it's the only thing I'm good at so I've stuck to it. People always tell animators: 'you must be the most patient people in the world'. But I don't know any patient animators. We're just persistent. You want to see it moving and alive at the end."

Things get even more intense at animation supervisor Will Becher's studio where I find him shooting the film's final scene. He shows me his suite of mouths for Wallace. Every puppet that speaks has a detachable jaw so that a variety of different mouth shapes can be attached. There is a different Wallace mouth for each phonetic sound - Becher picks out the classic "ee" mouth that gets used a lot for "cheese". It's much harder working with Gromit, he says, because he doesn't speak: "You have to get across what's going on inside his head with just two beads for eyes."

Becher has a little set of tools that he says all animators carry with them. Some of them look like dentistry tools. "Some of them (i)are(i) dentistry tools," he laughs.

Each week the animators - there are 28 on this film - meet to review their work. Becher says you can often tell who has animated which section because the characters in it reflect how they move themselves: the way they stand, for example, or a unique gait to their walk. These extremely subtle tics are considered a positive because they add warmth, but as a rule the characters need to remain as consistent as possible throughout. Becher plays me a short video to show how this is achieved: it shows Park and co-director Merlin Crossingham acting out a scene in person, to give the animators an idea of the expressions they want. It's quite funny to see Park saying "cracking toast Gromit" to the camera with maximum expressiveness. Does he have a thespian past we don't know about?

"No, no, no, I don't," says Park.

"I have a little bit," says Crossingham. "It helps to have an awareness of your own physicality, and to be able to brief the animator using ourselves rather than words. It's such a powerful tool. But we're not saying to the animators, copy us. It's more about being the springboard to find that nugget of a moment in a shot."

Park made his first Wallace & Gromit film, A Grand Day Out, as his NFTS graduation project. Originally he'd envisioned Gromit as a talking cat ("What on earth were you thinking?" laughs Crossingham), but fortunately found a dog easier to make out of plasticine.

Park says he still has to pinch himself when he sees how big his clay duo have become. "I'll hear their names on quiz shows, or whenever cheese is mentioned, and think 'gosh, I thought of those names at college off the top of my head!'"

Over the past 35 years, the way Aardman makes films has had to change. The sad death of Peter Sallis - who gave Wallace his charming Yorkshire accent - in 2017 means that understudy Ben Whitehead has stepped up. "Sometimes I've thought - that's Peter in the room," says Park. "It's the most uncanny feeling."

The addition of an Asian character in PC Mukherjee helps the film "reflect the Britain that we live in", says Park. And technological leaps are present not just in the Aardman studio itself but in the increasingly fancy inventions Wallace comes up with. But there is one thing that hasn't ever shifted: their dedication to jokes. "The smart gnome was really just an excuse to have Wallace say 'AI lad'," grins Crossingham.

My final stop of today's tour is with the scheduling department. Vengeance Most Fowl requires over 40 shooting units, 30 animators, 30 set dressers and around 200 people working on the film in total. Everything has to be planned in precise detail way before the animators get to work to ensure that the lighting, props, sets and camera operators are all in place when they do. And stringing this entire operation together? A load of boards and elastic bands.

"We knew you were coming," I'm told, as I rock up to the scheduling department. And it's true - among dozens of boards representing the days and weeks of movie production is one that has Guardian logos neatly printed on the panels. Plastered around my visit are marker penned instructions, post-it notes and more elastic bands - so many elastic bands. Each one, I'm told, represents a member of staff who has been moved from one project to another. Park says that they once tried organising things digitally instead but it wasn't as intuitive - so they went back to elastic bands.

I've no idea how anybody can make sense of it all. But whatever the method in the madness it clearly works: in the space of just a few hours I've met puppeteers, painters, camera operators and animators, made my own Gromit head and had a chat with Nick Park. And the minute it all finishes there's a taxi waiting to whisk me away back to the station. In the best possible way I feel like I've been sucked inside a great machine, whizzed around at a frantic pace and spat out at the other end. Rather like being inside one of Wallace's grand inventions, in fact.