For British director Paul King, the most exciting thing about making Paddington, the first feature film to tell the story of the small bear from Darkest Peru with a fondness for marmalade, was shooting at London's grand Paddington Station.

"It took about a year of planning because, obviously, the trains still need to run. They had to reprogram a ridiculous amount of the national rail network to make it all happen, because they're complicated things, railways, but they were so kind and so brilliant. Everyone at Paddington Station was just amazing," says King.

It proved to him the power of Paddington. Not only was the bear given access to one of the busiest railway stations in England, but he was also allowed to run wild through the halls of London's august Natural History Museum.

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The character helped King snag a shiny line-up of Britain's finest actors too, including Hugh Downton Abbey Bonneville and Sally Hawkins from Mike Leigh's Happy-Go-Lucky as Mr and Mrs Brown, Julie Walters as their eccentric housekeeper Mrs Bird, Peter Capaldi as deranged, pink-eyed neighbour Mr Curry, Little Britain's Matt Lucas as a gobby cab driver, and Geoffrey Palmer in a small role with large whiskers. That's just the live-action cast. On the animated side, thespian heavies Michael Gambon and Imelda Staunton are the voices of Paddington's aunt and uncle, while Ben Whishaw, known for playing a speccy Q in the last James Bond film, Skyfall, is Paddington.

Then there is Nicole Kidman as the evil, snakeskin-wearing, knife-edged, blond-bobbed taxidermist trying to get her hands on Paddington for her ultimate specimen. When King tentatively suggested her for the role, his casting director thought it highly unlikely she would be interested. Kidman's agent also thought she'd turn it down but her response was an instant yes, having loved the books as a child. She is not alone; the Paddington series has been translated into 40 languages and sold more than 35 million copies since A Bear Called Paddington by Michael Bond was first published in 1958.

If you pay attention to the film, in one of the early London scenes, as Paddington rides in his first cab, a distinguished older gentleman raises a glass to him from a pavement table. This is Bond, who invented the character while living in Notting Hill in the 1950s, and was closely consulted during the making of the film.

As well as directing, King wrote the script, which brings the story into the present day and introduces some new key characters, including Kidman's malevolent Millicent.

Many other writers helped whip the story into shape, and Bond provided suggestions on the different drafts. Knowing his bear so well, the older writer helped keep the tone of the film faithful to his stories. The Browns are loosely based on his own parents – if they had come across Paddington, Bond told King, his mother would have wanted to give him a bath and his father would have worried about the paperwork. King consequently wrote a scene where Mr Brown goes to the authorities about Paddington, but Bond felt it wasn't quite right. King ended up agreeing.

Something else wasn't quite right. For the voice of Paddington, King's first choice was another British star, Colin Firth, whose speech reminded him of the narrator of the first animated Paddington television series, Michael Hordern. It was this version that introduced King to Paddington as a child, before he learnt to read and devoured the books.

As Bond pointed out to him, Hordern was the voice of the narrator, not Paddington, but it took months of working with Firth until King admitted defeat: he wasn't the one.

"Colin's got too mature and manly and chocolate-y a voice," he says. "It's a gorgeous voice, but it just didn't feel quite right for the character."

Telling him must have been ... awkward?

"It was a little difficult," King says, but the actor had come to the same conclusion. "We had a very funny conversation where he said, 'Don't worry Paul, this isn't like splitting up with your girlfriend, it's fine.' If he was going to be out of work, I'd have worried, but I think Colin Firth will be fine."

Bringing the animated bear to life, says King, "was oddly like giving birth". In fact the gestation took twice as long – about 18 months from the first drawings of Paddington to the first on-screen test when he spoke and had fur added. This animated version is based on Peggy Fortnum's drawings in the first book. "They felt like the most bear-y bear that had been drawn, and it was the original and most useful for us," says King. "When it first came to life, especially when we found Ben's voice, I was in pieces. It was just incredibly beautiful and you go, 'I think this film's going to work because I believe in that bear'."

King has only directed one feature film before this, the darkly wacky and really quite obscure Bunny and the Bull in 2009. He is best known for directing The Mighty Boosh, the trippy cult television comedy series with a small but very loyal (some might say fanatical) legion of fans. Boosh-sters will recognise some of Paddington's more offbeat humour, such as the old-school explorer sequence that begins the film, or Kidman picking up a stuffed ferret instead of the phone.

The question that clearly must be asked is how King ended up directing a film like this, with an enormous budget and star-studded cast, adapting one of the most iconic children's characters ever written.

King laughs good-naturedly. "That's a very good question."

The answer is that David Heyman, the film's producer, thought he was the man for the job. Heyman, who produced Gravity, The Boy in the Striped Pyjamas and all the Harry Potter films, was struck by Bunny and the Bull, particularly its abstract, line-drawn sets that looked like the original Paddington television series.

King "wangled" a meeting with him and found they had the same ideas about how the film should be done. 

"You can imagine the not-very-good Hollywood version of it: Paddington is suddenly in a bomber jacket and a back-to-front baseball cap and he's rapping about marmalade," King says. "I wanted to do something faithful but I also thought there was really something beautiful we could do with London."

Paddington is set in the present day, as the Paddington books were set in the time they were written. King's London is Kodachrome-colourful, a heightened reality where jaunty calypso bands play on street corners and snow still buckets down at Christmas. The Brown house is a vintage-inspired fantasy any child would love to inhabit, let alone a furry young South American seeking refuge.

"I wanted a London where a bear would not feel utterly ridiculous walking down the street," King says.

His favourite films, which he wanted Paddington to emulate, are those that transport viewers, creating a world they don't quite recognise. "There's something amazingly visually beguiling about that," he says.

He has also created one of those rare and lovely creatures, a film that appeals equally to children and adults.

King thought a lot about why he responded to Paddington as a child, and came to the conclusion it was his outsider status.

"There's actually quite a big universal story here about somebody who has travelled round the world and tried to make a new home and is an outsider in a big scary universe. I think that's something lots of people connect to. There's a lot more to Paddington than you may immediately remember."