Everything has a colour in Nobody Likes Me!, Fay Weldon’s book for children. Sleep is brown and red and purple round the edges, a cry is pale blue, a roar black, a yelp white. I wonder, as the author sits on the green and gold sofa at her home in Hampstead, north London, what colour this conversation might be.

She is wearing a black dress and gold slippers and her voice is high and light. At first it seems hard to believe this is the same woman whose nearly 30 books include The Life and Loves of a She-Devil. And then her glance falls on the lighthouse on the back of her new book. “That really is very phallic, ” she murmurs, and laughs. It was the first of many small shocks.

Her book tells the story of a small boy called Rex, who has temper tantrums and rips up his yellow and mauve party invitation. He crawls into the black under his bed and pretends to be a bear. In his fantastical dreams he is always the odd one out. But he awakes to his mother’s new-found attentions and promises that the party will be fine. The language is poetic and the storyline as finely drawn as Claudio Mu$oz’s illustrations.

The title seems not to fit, though. “Nick, my husband picked it. It’s terribly rash to call a book something like this,” she says, happily. “It’s sort of a turn-off, isn’t it?” She wrote the book 15 years ago because she was asked to. But, having made the request, the publisher then rejected the work. A previous version was eventually published in 1989, but sank without trace. This edition will not suffer the same fate.

The story is improved and, as Weldon notes, the illustrations are be-autiful. It is also truly a child’s-eye tale. “Writing for children is slightly like writing advertising copy in that every word counts,” she says. “The relationship between sentences has to work exactly.”

Fay Weldon’s women are always noteworthy, and Rex’s mum does seem rather glamorous in her “clickety-clack silver sandals” and lovely red dress. Weldon disagrees. “Again, it is a child’s-eye view of clothing. She is wearing her best red dress and she’s been to the dentist, so her teeth are terribly white. She is ever so slightly horrific, because mothers are. It’s all quite terrifying.”

So where is father? “Oh, he’s at work.” Does the mother work too? “Oh no. She’s a very frivolous mum. She can’t stand the little boy. This is the difficulty. The little girl is very pretty but the little boy stamps in puddles and tears up invitations and is just a boy. And his trousers are too tight. ” This is said with a flourish. “The whole thing is about being inappropriately clothed, or mothers not loving you enough or mothers loving your sister, who wears a pink coat and is perfect.”

But the mother does make the boy a costume. Surely that was nice? “Yes, she does, but that may have been my editor, who insisted she show some of her good side.”

She suddenly asks if there are cannibals in the book. There are girls in pink gingham, an eagle in a greeny-white egg and an old-fashioned party with golden forks, but no cannibals. There were cannibals in a former version, she says. “Rex is left on a desert island and the cannibal asks him to tea. But then Rex realises he is going to be the tea. My editor talked me out of putting that one in.”

She leans forward. “Really, the dream is just an anxiety dream.” This is worrying, in that Fay Weldon’s aversion to therapy (her first husband left her during his) is well-known. She adds: “This is a sort of therapy book. It’s a self-help book that works subliminally. The child has these dreams and they make him angry. So if you write about them and explain them and solve them, it can help.

“Just because I don’t go to a therapist doesn’t mean I am against emotional literacy.”

There the lesson ended. And the colour? Gold streaked with bolts from the blue.

Nobody Likes Me! by Fay Weldon is published by Bodley Head, Pounds 9.99