It’s the first time they’ve all been together in a long time, as siblings Ross, Clemmie and Alice all live down south. That’s amazing,” says Thompson of the letter, which predates her six-year marriage to Branagh and was written from the flat they shared in 1988. When time’s up we’re ushered out along the corridors to a staircase that museum staff have identified as the exact one that Scheffler has depicted, where an excited gaggle of east London schoolchildren awaits. Royal corgis do not come out of it so well: Thompson depicts a stoutly entitled one chasing poor Jim out of the palace. She said: “It’s actually about canine conscience…because he does something that makes him feel guilty.

On what readers, young and old, should take away from reading Jim’s Spectacular Christmas, Emma replied: “I think it's a nice thing to read. Photograph: Suki Dhanda/The Observer ‘The question is not if, but when they will collaborate again’: Emma Thompson and Axel Scheffler. Humorously told and drawn though it is, this is a history book as well as a shaggy dog story – a delicate balancing act that became clear when it came to the portrayal of Queen Victoria, whose chest is being dabbed by her solicitous husband, Albert, to rid it of a tea stain when Jim catches his first glimpse of the royal family. He was playing Hamlet to her sister Sophie’s Ophelia and she wanted something to commemorate a moment in time. He wrote and narrated The Magic Roundabout, which targeted families as a whole, rather than just little ones.The actor was an early connoisseur of comic-book humour, who once wrote a fan letter to the creators of Asterix and received the reply that they were delighted to have made a small English girl laugh. This year, we are introduced to Sky Terran, a woman in flux – she’s just lost a job she loved, and has moved back to the town of Middledip, where she had happy memories as a child. I have a vague notion of what you charge for your work, which doesn’t seem to me to be enough,” it went on. Though they never actually met in person, they exchanged gifts on the birth of their first children; hers to him was a food hamper; his to her was a picture of a pig wheeling a pram. Then she trumps it, by announcing that she still has the envelope in which Scheffler sent the two pictures.

And now she has collaborated with Scheffler, the illustrator associated with Julia Donaldson’s picture books, on this Christmas tale. But she agreed to this one because it was pitched to her as an invitation from Henry Cole himself, just as the three Peter Rabbit books she has previously written were pitched as invitations from Peter: “There’s still a little bit of me that thinks it was Peter Rabbit himself who asked me,” she says. She draws the vowel out into a camp diphthong as part of a running joke with Scheffler as to which of them will seem most exciting to the children for whom their new book is intended: the actor who starred as Nanny McPhee and now as Mrs Trunchbull in the film of Matilda the Musical or the illustrator of the mega-selling Gruffalo books.

As well as adapting the joyful Nurse Matilda books into ther successful Nanny McPhee films in which she played the lead, she has written beautiful books for the Beatrix Potter estate, gently updating the author’s voice.

So I always go, if I'm writing something for children, generally speaking, I go and do it in Scotland, because it's quiet. With illustrations from Axel Scheffler (best known for his work with Julia Donaldson, including The Gruffalo), Jim’s Spectacular Christmas tells the tale of a grubby pooch who is losing his sight, and so liberates an eyeglass from a very regal acquaintance while delivering his master’s latest invention – Christmas cards.

The guilt present, that guilt gift, the fact that you feel guilty because you're not with your parents, auntie, siblings, Christmas is just a time that's absolutely built for guilt. An icon of her craft, Cradock became synonymous with Christmas cooking, due to her no-stress, cost-effective extravagance.