Most mornings, when in London, I climb the stairs of the house where I grew up during the 1950s and 60s to what was my bedroom, now my mother’s studio – and there she is, at the drawing board, aged 92.

The woman that countless grandparents, parents and children call Shirley Hughes and Philip Pullman calls “a national treasure”, I have the honour of calling Mum.

The view beyond the winter branches has changed: cranes over White City, and Grenfell Tower. But the porcelain palettes of carefully mixed colours, and the design on silver tubes of Winsor & Newton paint, are as they were when I was a child and Mum would write and illustrate her children’s books, listening to the Beatles, Billie Holiday and Edith Piaf.

Sixty years later the task in hand these past months has been quite something: Dogger’s Christmas. It’s a sort of remake of Mum’s best loved and most successful book, Dogger, about a boy, Dave, who loses the cuddly toy on which he feels his life depends, the ensuing trauma – and resolution.

It feels a bit like a greatest hits album. Mum has done other books for this season of the year: Lucy and Tom’s Christmas, one of her earliest, and Alfie’s Christmas, featuring her longest-running character. But she has never before infused Christmas Day with that unlikely superhero, a stuffed toy dog cuddled with such intensity that his fur has worn off.

Last March, Mum had a fall and it was a worrying time. I can’t say I was surprised at her recovery, but Dogger’s Christmas, announced by Penguin Random House last week, will be, among other things, testimony to Mum’s resilience of body and spirit. “I have to get back to work,” she would say. So back to the studio: “My publisher said they wanted another Christmas book, and what better offering to my readers than a Dogger drama on the big day?”

The original Dogger was published in 1977. Dave mislays his companion and is distraught, only to find Dogger on sale at a school fete for 5p. By the time Dave finds his family, it is too late – Dogger is sold. But his athletic sister Bella wins a prize – a huge teddy bear – with which she duly entices Dogger back from his new owner.

The book has origins in two true stories. Mum recalls the first: “My mother, a widow, did not drive, and we were being taken in a taxi – a converted hearse – by a man called Eric Barrington from the Wirral for holidays at Llandudno Junction. The window was ajar and for some reason I threw my koala bear, Oscar, out of it. I have no idea why. Not for miles did I raise the alarm. When I did, we went back, Mother and Mr Barrington searching the roadside to no avail.”

Then the second: the afternoon I left my indispensably favourite teddy bear in then-tatty Holland Park. “It was just awful: Dad going down there with a torch, climbing in, searching – we never found the bear; you didn’t sleep for ages.”

Dogger really exists. I was given him for Christmas 1959 (I think) by my Irish great-uncle, Hugh Hynes, a general practitioner. Says Mum now: “Little did Uncle Hugh know …”

She made Dogger the hero of her adapted tale, giving these cruel real-life narratives a fictional happy ending. The book won the 1977 Kate Greenaway prize, the children’s books Oscar, then 40 years later the “Greenaway of Greenaways” – a bit like being the all-time hall-of-famer in the baseball hall of fame – weeks after my father’ death, while Mum was working on another book about a toy lost in this-time-enchanted Holland Park: Jonadab and Rita.

“Dogger has become something of a celebrity,” says Mum now. “He was put in a glass box, on tour, at the Ashmolean in Oxford and Liverpool Walker Art Gallery. He has one ear flopped down, as it should be, and another that was cocked up from years of cuddling and has remained that way after 60 years. His eyes are rather far apart, which I think makes him especially endearing. He’s retired from the celeb circuit now, living in a shoebox, only coming out for the occasional photoshoot” – including last week for the Observer.

Why did the book do so well? “So many children know that dependence on, and love for, a cuddly toy – and the trauma of losing it. But parents too: all hell lets loose when something like that happens in a child’s life, and no one can sleep.”

But there’s also this: “The real story, though, is about Bella, her kindness and self-sacrifice, understanding what’s really important in life: Dave’s old dog and all it means to him, rather than this big, new, shiny bear she’s won. She’s a good sister, and a good human being.”

Those who reckon that lightning doesn’t strike twice, think again. Dave is the same age now as he was in 1977, and dammit if Dogger doesn’t go missing again, on Christmas Day.

Some might think that part of the appeal in Mum’s books is that life is the way it used to be, or should be – not how it is now. That could be true of Christmas, too. But it’s not as simple as that.

Mum is not especially religious, but beneath her books, apparently simple, cuts a riptide which could be described as “christian” with a small “c”. “Christmas in this book is more about family and home than cheap booze and shopping,” she says. “Dave, Bella and Mum go to visit an elderly neighbour who lives alone while – please note! – Dad cooks. It matters a lot that the children know that Christmas is about the baby in the manger, the birth of Jesus and all it stands for. Whether you are Christian or not, there are universal values associated with Christmas.”

Yet there’s always stress on the day. “Alfie’s sister, Annie Rose, throws a temper, over-excited; there’s a battery lacking.” All this is nothing, however, compared with Dogger, almost forgotten in the bustle, buried under a pile of wrapping paper – then nowhere to be found.

Will Bella do it again? Is Dogger gone for good this time? “I’m not telling what happens,” Mum rolls her eyes, “but it’s a close shave.”

• Dogger’s Christmas will be published by Penguin Random House in autumn 2020.