And the moral to this tale?

It's that there doesn't always need to be a moral, as Gruffalo creator Julia Donaldson tells Kate Whiting

On a sunny summer day, the UK's bestselling author Julia Donaldson is deservedly relaxing in her new garden.

She and her husband of almost 42 years, Malcolm, have just moved from their family home near Glasgow to a small Sussex town and their new house, she excitedly reveals, has three baths.

She's not showing off her wealth, however - the baths represent potential hours of inspiration.

"You have to put in time at your desk, of course, but so many of my ideas have gelled when I've been in the bath," she explains. "In the new house, there are three baths, so I can get different ideas in each one!"

Years ago, it was another bath - one with clawed feet belonging to a friend - that gave the 65-year-old grandmother the idea for one of her latest children's books, The Flying Bath.

"The idea lay dormant for about eight years because I couldn't think what would happen, and then somehow I hit on the idea [that] the bath goes around supplying water, a bit like a fire engine, to animals, like the thirsty kangaroo and the baboon who's tree's on fire."

It's incredible to think someone so creative and prolific - Donaldson has written 160 titles and sells more books than JK Rowling - only had her first children's book published when she was 44.

Before then, she'd written songs that were sung by children's TV presenters on shows like Play Away and, as luck would have it, just as the work started to dry up in the early 90s, a publisher got in touch to ask whether her song, A Squash And A Squeeze, could be turned into a picture book. The illustrator was Axel Scheffler, who collaborated with her again six years later on what has become her best-known work, The Gruffalo.

Donaldson had no idea how popular the book would become.

"At the time, there weren't very many adventure-type picture books. There were quite a lot of moralising books, or to help a shy child smile and then she'll make friends, which can be done well, but they can sometimes be a bit soppy.

"I thought people will think The Gruffalo's a bit weird. But maybe I just struck lucky and it was time for a change of direction, because now there are loads of rhyming books about monsters."

Nowadays, you can barely walk down the high street without seeing the latest Gruffalo merchandise on display.

"I get sent a box every few weeks," admits Donaldson, "so it means I can give it away, either to my grandchildren or if a nice plumber comes round and they say they've got my books, I give their little girl something."

She and Scheffler have just worked together again on The Scarecrow's Wedding.

As children's laureate from 2011 to 2013, Donaldson backed libraries and encouraged children to read aloud, but she doesn't feel beholden to moralise in her tales.

"I'm just trying to tell a story. Obviously it's not the world as it is because you get talking animals, but I'm certainly not trying to teach children to share or anything like that."

And she's a firm believer that it doesn't matter what children read, so long as they do read.

"I remember when The Beano would pop through the letterbox and my son would seize it and read it on the loo. I certainly didn't look down my nose at a comic, as opposed to a book."

Donaldson had three sons with her retired paediatrician husband Malcolm, who she met at university in Bristol. Her eldest, Hamish, killed himself in 2003, aged 25. He'd suffered severe psychotic episodes growing up and was diagnosed with schizoaffective disorder. Donaldson describes him as a "lovely, lovely boy" that "no-one could cope with from the word go". She developed the ability to "compartmentalise" and, in 2009, wrote a book for older children, Running On The Cracks, dealing with mental illness.

Her younger sons Alastair and Jerry are both married and have given her four grandchildren (with another on the way), who she now delights in reading her books to.

"It's funny, I'm so used to reading my stories to big audiences, it's strange to be reading them one-to-one like I used to with my own children.

"Poppy, in particular - she's the four-year-old - gets very hooked on not just my stories, but she absolutely loves books, especially if there's some disaster coming."

Malcolm now accompanies Donaldson around the world on tours of concerts, where they sing and act out her books (a show based on her award-winning book What The Ladybird Heard - her tale of criminals trying to steal from a farmyard - is touring the UK, but Donaldson and her songs aren't included).

She has her hands full with her latest books though, preparing for two sold-out performances at the Edinburgh Festival and answering her fan mail, which takes a day a week and can be a cathartic experience.

"I've had a surprising number of letters from parents whose children have either died or are dying, or from an older child who loves my books," she says.

"There was a really sad one from a girl with leukemia, who did a wonderful recording of herself reading and I made a video to send back to her saying how great it was. Sometimes I'm just in tears when I'm reading my fan mail.

n Tour dates: September 9-11, Theatre Royal, Glasgow.