If you wanted to explain a certain kind of Englishness to a Martian, you could do much worse than sit him down with a DVD box set of Wallace & Gromit. Note, you'd have to say, the bald, all-purpose Northerner in the knitted tank-top, with the toothy grin almost wider than his face and the love of cheese and crackers. Note the sidekick, a Dogstoyevsky-reading dog. Note the two-up two-down, the vegetable patch, the baker's van, the church tower, the endless pots of tea. And note, you'd have to add, that this extraordinary duo, Betjemanesque exiles from a lost England reminiscent of the 1950s, are made out of Plasticine. And that their fans include Prince Charles and the Queen. And that their most recent outing, on Christmas Day, attracted more than 14 million viewers.
The Martian might then be slightly less surprised to learn that adults (and children, but I suspect more adults) can now wander round Wallace & Gromit's sitting room, kitchen and bathroom. They can gaze at their wallpaper and twiddle the knobs on their machines. "It's quite worrying, really, to see it life-size," says my companion, "because it's like I'm a model on the set when I walk around, that I'm the size of Wallace."
Well, yes, that must be very strange indeed. For my companion is Nick Park. Twenty-seven years ago, while a student at the National Film and TV school, he created Wallace & Gromit. It must be quite a shock to see his student project taking over a large space in one of our national institutions. For this isn't a theme park à la New Forest Lapland; it's the Science Museum. And the life-size sets are part of a new exhibition, Wallace & Gromit present a World of Cracking Ideas, designed to "tell the story of innovation" and "inspire people's creativity".
The exhibition is a partnership between the Science Museum, Aardman Animation (the company for which Park works) and the Intellectual Property Office. Inevitably, it's called an "experience". Inevitably, the organisers keep telling me how "exciting" it is. The press officer is thrilled by the "ideas machine", a huge contraption into which you chuck an idea, scrawled on a piece of paper, see it carried along a network of wires called a "brain wave" and then collect, at the other end, a paper thinking-cap – which bears no relation to your original idea. The man from the Intellectual Property Office proudly points out a karaoke shower, a slide inspired by Wallace's tipping bath, posters about pirating (of the intellectual, not the swashbuckling kind) and a garden that is, of course, all about sustainable energy. I'm sure for children it's lovely. But what really is thrilling is to see some of the tiny original Wallace & Gromit sets – and what really is thrilling is to encounter the brain behind them.
"It's a great privilege for me," says Park, "because I used to come round here as a student because I would just love all the machines and all the inventions. I love the shapes of a lot of the objects, especially from the Fifties and before; you know, rockets and stuff. So to have my creations actually fronting an exhibition is incredible."
If Park isn't the size of Wallace – that is, tiny – he's not very big either. And if he doesn't look quite like Wallace, there are shades of him in the smiley face and (now, at 50) slightly balding head. In the commentary on the DVD of Wallace & Gromit's Christmas outing, A Matter of Loaf and Death, he talks about acting out the parts for the animators. The obvious word to use for his face – this, after all, is a man who loves puns – is, I'm afraid, animated. It switches, in a moment, from blinking shyness to boyish grin. And his arms, clutching both a coat and, obediently, my tape recorder, veer between nervy immobility and enthusiastic waves.
"My dad used to spend time in the shed building things," he says, "but I also used to love stories – HG Wells, The Time Machine, you know, those stories which were all about Victorian inventors who built rockets and things like that. I think I used to want to be an inventor as a child and I'm sort of living that out. I used to keep a box under my bed with broken toys and old electric motors." Park grew up in Preston, which became the setting (in a 1950s, Hovis, Bisto sort of way) for all the Wallace & Gromit adventures. Now, there's a college campus named after him and a street named after his most famous creations there .
Clearly, Park took his Blue Peter assignments a little more seriously than the rest of us. He even has a gold Blue Peter badge. "It must have been about '97," he says, "when I got my CBE. I remember on the news they said, 'What's it like?' and I said, "It's like a Blue Peter badge for grown-ups,' and the next thing I knew Blue Peter asked me on." So which is he more proud of? "The Blue Peter badge, obviously! That's the thing I'd worked for since I was young."
Luckily, the machines he made didn't actually have to work. When he was 13, his father gave him a camera and he started making films featuring the family's pet hen, Penny – and he discovered that "with animation, it just has to look as if it works". He went on to study communication arts at Sheffield Art School and then animation at the National Film and Television School in Beaconsfield. It was there he started working on his first Wallace & Gromit film, A Grand Day Out. In 1985, he joined Aardman, where he finally finished it. In 1990, it was nominated for an Academy Award (otherwise known as an Oscar), but it was another of Park's projects, Creature Comforts, which won. Park forgot to bring a bow tie for the ceremony, but made one out of cardboard. He wore a cardboard bow tie when Wallace & Gromit's next two outings, The Wrong Trousers and A Close Shave, won Oscars, too.
Perhaps it's not surprising that Hollywood, in the form of Steven Spielberg's Dreamworks, beckoned. Chicken Run, the first film in the Aardman-Dreamworks partnership, took more than $250m. The Curse of the Were-Rabbit, the second (and the fourth Wallace & Gromit adventure) won yet another Oscar, but box-office takings were disappointing. After the third film, Flushed Away (not one of Park's), the collaboration faltered. "Creative differences" were cited. I don't, I have to say, like to think of Nick Park being bossed around by a bunch of guys like the ones in the Orange switch-off-your-mobile cinema ads. I don't like to think of Wallace & Gromit being subject to focus groups. It's all a bit far away from that English shed.
"Part of me still does want to be that tinkerer in the shed," says Park, "doing it myself, but that would take years." A Grand Day Out took, to be precise, seven years to make. Even now, with teams of animators working round the clock, it takes a day to produce about one second of footage. For The Curse of the Were-Rabbit, Park actually had to run three-week courses for the animators, introducing them to the myriad complexities of Wallace & Gromit's universe, the myriad complexities, in fact, of Nick Park's head. Even so, it sounds like one of the most torturous artistic processes in the history of mankind. Doesn't that frustrate him?
Park looks puzzled – almost cartoon-puzzled. "I don't find it takes that long," he says. "That's the funny thing. It's like painting or something. You don't actually look at it in terms of the cost. You're just thinking more about what you want to achieve. There might be a three-second shot that's going to take two days to do, and you're working with 30 animators, shooting at the same time on all these various sets. The joke, the timing, has to be just spot on and you've got to be very precise about what you want. So that's why we resort to acting it out on video."
And does he, after all that acting, ever actually feel like Wallace or Gromit? "I suppose so! Yes. I see family resemblances," he adds, "sometimes. On the first Creature Comforts, sometimes I would see a member of my family in the face. In the polar bears, actually. I remember seeing my niece." Lest anyone think that to see a niece in a polar bear is considerably more crackers, to use a Wallace word, than to see the world in a grain of sand, let them sit down, with a nice cup of tea, and muse on the miracle that is Creature Comforts: the Scouse cat, relaxing, after a hard day's stretching, by the radiator; the Scottish pandas bickering about the washing up; the zoo-bound, Brazilian-accented jaguar lamenting his captivity and dreaming of swimming in a tropical country. Above all else, these Plasticine animals, lip synched to real dialogue in a range of regional accents (and used in an advertisement for the Electricity Board) radiate humanity.
So, of course, do Wallace & Gromit. Park's father, who died of lung cancer in 2002, was often compared with Wallace and, says Park, "loved it". Park, on the other hand, has been compared with the omni-competent Gromit. A psychoanalyst might be tempted to see the two characters as warring parts of himself. Is there any of Wallace in Park? "I hope not!" he giggles. "He very much has an idea and does it, and doesn't think. He lacks sensitivity, I guess. But I suppose in terms of... well, just to make these films, you've got to be a tinkerer, like Wallace, you've got to be inventive and resourceful."
And what's it like to go from tinkering in a shed, or a basement, to lunch at Buckingham Palace – the Queen, apparently, insisted on sitting next to him – or dinner with Naomi Campbell at the Oscars? "I never thought playing with Plasticine would lead to such a glamorous lifestyle, to be honest. What's great is that I often meet Hollywood stars and they always end conversations by saying, 'If you ever need a voice...' It makes it quite easy to approach anybody, really. But," he adds, "it's not glamorous, really. You spend your time in the dark, in studios without sunlight, and you come out occasionally."
And the truth is that most of it isn't that glamorous, and Nick Park wouldn't want it be. This multi-millionaire lives on his own in a two-bedroom cottage outside Bristol. He spends holidays in his camper van. He likes watching the dragonflies and the frogs in his pond. On Sundays, he goes to church. He feels grateful, he says, as if he didn't dream them up, to "have met" Wallace & Gromit. "If you ask me what Wallace or Gromit would say," he says, "I don't know, because I'd have to almost ask them."
And do they, I ask, feel a bit like his children? Nick Park, great English eccentric, perfectionist celebrant of the English amateur spirit, creator of heartbreakingly humane gentle comedy, gives a shy smile. "I have thought that," he says. "Yes."
Wallace & Gromit present A World of Cracking Ideas opens tomorrow at the Science Museum, London SW7 (www.sciencemuseum.org.uk)