Funnily enough, I find it harder to write not in verse, though I feel I am now getting the hang of it! My novel THE GIANTS AND THE JONESES is going to be made into a film by the same team who made the Harry Potter movies, and I have written three books of stories about the anarchic PRINCESS MIRROR-BELLE who appears from the mirror and disrupts the life of an otherwise ordinary eight-year-old. I have just finished writing a novel for teenagers. Malcolm, whom she mentions frequently, is the only person with whom she shares early ideas and drafts, discussing things while walking near their home in West Sussex, and showing him “half-baked manuscripts”. Did they instantly know, when Scheffler made the drawings for A Squash and a Squeeze almost 30 years ago, about an old woman who thinks her house is too small, that they’d found each other’s work soulmate?

We have sailed past our allotted time by now but I have one last question from my three-year-old: why, at the end of A Squash and a Squeeze, does the pig look angry but the other animals don’t? She always replies to children’s letters. “And they haven’t changed over the decades. It’s always the usual mix of ‘Where do you get your ideas from?’ to ‘Why do you wear such funny shoes?’ I love it, because adults are probably dying to ask about my shoes but they just say, ‘Are you inspired by Tolkien?’”Though, she admits, she's running out of creatures for Scheffler to draw. "I do think sometimes about gargoyles or a sphinx or something," she says. "It's getting harder and harder, actually."

He tends to read things out loud in what we call his Dylan Thomas voice, this sort of cod Welsh accent, and it always sounds quite good when he does it.” You’ll have to ask the pig, I’m not responsible for my characters!” laughs Scheffler, and Donaldson nods: “It’s nice when children see things in the books I’m not aware of. You know they’re really looking at them.”They are the brains behind dozens of picture books including Room on the Broom, Tabby McTat and, of course, The Gruffalo. One of their latest books together is The Baddies — about a witch, a troll and a ghost who like being bad. The baddies have ended up as a troll, a ghost and a witch, as well as a little girl who isn’t frightened by them at all, and I mention to Donaldson that I think it’s clever how it rightly observes that children are rarely scared by what you expect (my own son, for example was for years inexplicably terrified by the owl in The Gruffalo). “Oh that’s so true. We did a show recently where a child was not fazed at all by the dragon but was so scared of the wind.” What does she think children are looking for in a memorable picture book? “You know, you can’t generalise about young children. I have nine grandchildren and they all have different tastes. But a satisfying ending that isn’t totally predictable is important. And the language.” When a little girl moves into a nearby cottage, the Baddies can’t wait to scare her out of her wits. In The Baddies, the witch, the troll and the ghost come a cropper when a little girl refuses to be scared by them. Although it’s never mentioned in the story, she is of south Asian heritage. Is this the first time they’ve featured a non-caucasian main character? We are experiencing delays with deliveries to many countries, but in most cases local services have now resumed. For more details, please consult the latest information provided by Royal Mail's International Incident Bulletin.

She wasn’t unhappy, she adds, just sensitive. “I just couldn’t understand other people, and even when I was about 10 I would always have one little cry every day.” One year her father gave her a poetry compilation, A Book of 1,000 Poems, and she decided to become a poet (she cites Shakesapeare as an influence and has recently written a story in iambic pentameter for the first time). The Smeds and the Smoos wasn’t about Brexit, it was just Romeo and Juliet with a happy ending,” Donaldson insists. “I never start a book thinking, ‘I want to teach the world to stop being at war.’”The ghost tries to scare the little girl in her bedroom — she offers him a warm bath and a cup of tea. For his part, Scheffler says he prefers to draw fairy tale stories and fantastical creatures. "I find it easier to illustrate a story like that," he says. "I don't think I'm very good at observing the everyday, modern life."