It is -15C and snowy outside but unusually relaxed and welcoming inside a grand building on the corner of Senate Square in Helsinki where a preview is taking place of the much-anticipated TV animation Moominvalley. The most expensive of its kind in the history of Finnish television, the series is the creation of Oscar-winning director Steve Box (Wallace and Gromit) and executive producer Marika Makaroff, of the company behind The Bridge (spoiler: it is much sunnier in Moominvalley).

That evening no one is left in any doubt as to the central place of Tove Jansson’s Moomins in Finnish culture as the vice president, clutching two Moomin mugs, tells the audience they are Finland’s “crown jewels”. “Moomins is a religion,” agrees scriptwriter Mark Huckerby when we meet – along with his longterm writing partner Nick Ostler – the following evening in a bar with the un-Moominish name of Liberty or Death. The award-winning duo have previously taken on Peter Rabbit, Thunderbirds and Danger Mouse, but nothing quite prepared them for the daunting task of bringing Jansson’s much loved troll family to life. “Moomins is so head and shoulders above any of those others.” says Ostler. “It’s terrifying.” It was easy to get actors such as Kate Winslet on board, he says, because of their shared passion for the philosophical hippo creatures. Rosamund Pike was cast against her icy Bond/Gone Girl type as the cosily droll matriarch and, in inspired casting, Will Self is the voice for the curmudgeonly philosopher Muskrat.

Since Jansson’s death in 2001 there has been a resurgence of interest in her work, including reissues of the Moomin books with their original artwork and publication of her lesser-known fiction for adults, culminating in exhibitions and a biography in 2014 to mark the centenary of her birth. Literary devotees include Ali Smith, Sheila Heti and Jeanette Winterson; Terry Pratchett called Jansson “one of the greatest children’s writers there has ever been”, and Philip Pullman believes that she should have been awarded the Nobel prize for literature. Children’s author Frank Cottrell-Boyce sums it up: “I lived on this great big housing estate in suburban Liverpool, from a working-class background, and somehow this bohemian, upper-middle-class Finnish lesbian eccentric felt like she was speaking directly to me.”

One in four people in Finland watched the first episode when it was broadcast earlier this year

But whether Jansson speaks to generation Peppa Pig (in some ways a much simplified porcine progeny) is another matter. Like so many popular characters – Paddington, Winnie the Pooh, Miffy – the Moomins are perhaps more often found on a mug or a tea towel than between the covers of a book. And, judging by last year’s designer Moomin cashmere jumpers and the new spring collection from Uniqlo (the Moomins are huge in Japan), Jansson’s characters show no sign of going out of fashion. It is hoped that the all-singing all‑dancing TV adaptation – featuring artists such as Alma, First Aid Kit and MØ on the soundtrack and 3D CGI – will attract a new audience when it launches this Easter. An astonishing one in four people in Finland watched the first episode, Little My Moves In, when it was broadcast earlier this year.

Like so many Brits who grew up in the 80s, Huckerby and Ostler were only familiar with the Moomins from the cult cartoon. “Then this massive box arrived from Finland,” recalls Huckerby. “There were the novels, plus the comics, plus Tove’s biography, plus short stories and other things she’d written.” Their brief, Ostler explains, was “to create an authentic adaptation of the nine novels”, although they were fairly relaxed about taking “bits and pieces from different stories” as well as the long-running cartoon-strip and mixing things up. “Jansson retold some of the stories in different forms over the years, which is quite useful if you are adapting something because it makes you feel better about the changes you have to make.”

Watch the official trailer for the new Moomin series

Night of the Groke, the episode we watched at that premiere, has all the elements of a classic Moomintale without being faithful to any one story. Moominpappa proposes going on one of his free-spirited camping trips, and Moominmamma cheerfully concurs: “Your father has decided to lead a life of wild abandon … again! But don’t worry, I’m sure we will be back by morning.” She packs his favourite pillows, just in case. Moomintroll, “his usual brave little self”, overcomes his anxieties at being left alone by confronting the infamous Groke, a mysterious grey shadow who freezes everything in her wake. It has become a representation of our own fears, “a kind of walking manifestation of Scandinavian gloom”, according to American novelist and children’s fiction expert Alison Lurie. “It’s something that people do remember from their childhood,” Huckerby says. “Friends always say: ‘Are you doing the Groke? That one gave me nightmares when I was a kid.’” But even here empathy is extended: “I suppose she’s just looking for a little warmth in her life,” Moomintroll muses. And each 22-minute episode is bursting with Moomin wisdom such as: “The only thing you really need to fear is fear itself.”

It is striking how much fear shadows the novels: for all the sunshine and picnics, menace lurks behind every bush: like a skater on ice, Jansson is always aware of the murky darkness just inches below. Of her success Jansson wrote: “Daydreams, monsters and all the horrible symbols of the subconscious that stimulate me … I wonder if the nursery and the chamber of horrors are as far apart as people think.” As Huckerby observes, the novels “go to some very dark places” and they have tried to reflect this in their adaptation. “It is being billed as prime time drama for all the family,” Ostler says. “It’s not a kids’ show.”

The Moomins and the Great Flood, the first in the novel series, begins with Moominmamma and Moomintroll looking for a place to live after they have been forced to leave their home behind the stove due to the advent of central heating (progress!). They are also searching for poor Moominpappa, feared drowned. The next, Comet in Moominland, tells how the family shelter from what threatens to be nothing less than the end of their world. In both books, we encounter boatloads of “small, pale creatures”, the Hattifatteners, doomed to wander from place to place, and “crowds of fleeing creatures”.

Moomin, with Thingumy and Bob, believed to represent Jansson and her lover Vivica Bandler. Photograph: © Moomin Characters ™

Originally published in 1945 and 46, but begun in 1939, those first two books were Jansson’s attempt to escape the terror of the second world war: “My very first happy ending!” as she wrote in her introduction to The Moomins and the Great Flood. While these existential dangers can be interpreted in the context of the 1939-40 winter war – the Soviet bombers over Helsinki and threat of invasion – they resonate all too strongly with current conflicts, the plight of refugees and, with uncanny presentiment, today’s ecological crisis. “‘Oh, dear, oh dear, the beautiful sea quite gone ... No great storms, no transparent ice and no gleaming water reflecting the stars. Finished, lost, gone!’”

But it was Jansson’s “universal themes” about growing up and domestic life that really drew the scriptwriters. “She made very funny books about the family. There are very recognisable types, that everyone can relate to easily,” says Ostler. Identified only by those most gender-specific of accessories, a top hat and handbag, Moominpappa and Moominmamma might seem to conform to sexist stereotypes (there was a bit of a backlash in the 70s). However, as with so much else, Jansson is gleefully subversive: Mamma might be wearing the pinny, but she’s very much in charge, benignly ruling Moominvalley from her handbag (more Mary Poppins than Margaret Thatcher), pulling out everything from dry socks to tummy powder – you never know when you might need an egg whisk – while Moominpappa is always off on one of his adventures or deep into his memoirs. (The bumbling, bumptious father and breezily competent mother will be recognisable to anyone familiar with Peppa’s Daddy Pig and Mummy Pig, with their trademark specs and fluttering eyelashes.)

Mamma and Pappa were clearly based on Jansson’s own parents, sculptor Viktor Jansson (“The Artist”) and her beloved mother Signe Hammarsten-Jansson (“Ham”), an illustrator; determinedly liberal bohemians, who seemed happy to conform to traditional gender roles – although it was her mother who actually put food on the table. As with the Moominhouse, their doors were always open to a succession of colourful visitors.

As the apocalypse looms Moominmamma is busy arranging shells around her flowerbeds, while cakes are baking in the oven

Originally conceived by her uncle as a menacing bogeyman to scare the children from stealing jam in the pantry, Moomin was sketched by Jansson on the toilet wall, “the ugliest creature imaginable”, in an argument with her brother about the philosopher Kant (theirs was not a typical upbringing – they had a pet monkey, for a start). He seems to have made his first public appearances alongside Hitler (of all the unlikely pairings) in wartime cartoons for the satirical magazine Garm, for which Jansson worked for 24 years. “What I liked best was being beastly to Hitler and Stalin,” she wrote. With longer noses and an angry glare, the original Moomins were altogether meaner creatures than the snouty smiley (a feat given they don’t have mouths), fondant-icing figures, famous for their gentleness, generosity and good humour, into which they evolved.

Finn Family Moomintroll, the third breakout book and still the most popular, published in 1948, is a much brighter affair. It is here that we encounter the inseparable Thingumy and Bob, carrying around a suitcase containing a secret ruby, to them “the most beautiful thing in the world”, believed to represent Jansson and her lover at the time, theatre director Vivica Bandler. (Homosexuality was illegal in Finland until 1971).

Life chapters … Tove Jansson drew on her experiences of love and loss. Photograph: Per Olov Jansson

But it is not until the sixth book, Moominland Midwinter (1957), with which season one of the TV series ends, that we meet cheery Too-Ticky. With a talent for reading the weather and calming fears, she was inspired by Tuulikki Pietilä (Tooti), the love of Jansson’s life. The couple would spend each summer on an island off the Finnish coast, without electricity and accessible only by rowing boat (there are glorious photos of Jansson swimming with a flower garland in her hair). Poor Moomintroll wakes too early from the annual Moomin hibernation, but can’t rouse any of his family and winter has arrived: “It’s dead. All the world has died while I slept. This world belongs to somebody else whom I don’t know.” For Jansson, it was her book about “what it is like when things get difficult”. “It’s a real coming-of-age story,” says Huckerby. “It is really about him becoming independent of his family,” Ostler continues. “She wrote it at the time when she was becoming more independent of her own family because she’d met Tuulikki.”

The final two books turn more melancholy, reflecting Jansson’s darkening state of mind. In Moominpappa at Sea (1965), Moominpappa has a midlife crisis and decides to relocate the family to a remote lighthouse. Huckerby believes it is “probably the greatest book written about depression that there has been”, and, both writers agree, “her masterpiece”. It was also the one that confounded them to begin with, and now, having read it some 15 or 16 times, they are still discovering new things about it. “The writing frustrates you,” Huckerby says, “because you keep going back, he keeps making the same mistakes, and you realise that it is a kind of cycle of depression and you can’t get out of it. It’s a profound work.”

“It’s also very funny,” Ostler adds. “It’s like a terrible British holiday where it rains all the time: you are trying to be cheerful but it’s dreadful.” Few artists do rain like Jansson – she was influenced by Van Gogh, after all – and, as Ostler points out, there’s a wonderful drawing of the family picnicking on a tiny beach: “It is sheeting down, on this bleak, bleak island. There’s something very blackly comic.”

The TV series takes us up to the final novel Moominvalley in November (1970), the saddest of them all, written just after the death of Jansson’s mother. “It is a book about death, really,” Huckerby says. “And about the loss of the Moomins. They aren’t even in it as the main characters. It’s a book in which everyone is waiting for them to return.”

It is this strangely comforting combination of catastrophe and everyday cosiness that makes the Moomins so enchanting and enduring. The Moomin books are survival stories: no problem is so great it can’t be made better by a cup of coffee and a cuddle. As the apocalypse looms Moominmamma is busy arranging shells around her flowerbeds, while cakes are baking in the oven: “She will know what to do,” says Moomintroll. So much literature is about escape from the family, but here it is always the point of return, a place of safety: “You must go on a long journey before you can really find out how wonderful home is,” Moomintroll reflects.

This loving, lavishly produced adaptation couldn’t be more timely: never has there been a better moment to introduce the Moomins, with all their optimism, openness and hospitality, their deep connection with nature and anti-consumerist ethos (without ever being pompous – with the exception, perhaps, of Moominpappa), to a new audience, and hopefully readership. As Ostler says, “They go through everything – floods and earthquakes and volcanic eruptions, comets. It all happens, but they kind of face it all with a smile.”

• Moominvalley is launched on Sky 1 and Sky Kids on 19 April.