Nothing is quite as it seems in Polly Dunbar’s house on Hove seafront.

The kitchen is framed by theatrical velvet curtains, there’s a briefcase in the shape of a Scottie dog and the dustpan and brush is a giant scallop shell.

When the doorbell buzzes to herald the arrival of The Argus’s photographer, she makes a quip about it being the noise of the ejector seat.

It’s a whimsical kingdom (queendom?) befitting a woman who makes a living from daydreaming or, as she puts it, “sketching and writing and doodling and hoping”.

Dunbar is a leading light in children’s publishing, a writer and illustrator whose magical stories about mute penguins and sad little girls, shoedwelling babies and vain chickens are loved by children and parents alike.

Since graduating from Brighton University’s prestigious illustration course in 1999, she has written and/or illustrated dozens of books from 2004’s Flyaway Katie who literally paints her blues away, through David Almond’s moving My Dad’s A Birdman, up to her current Tilly And Friends series, a sort of house-share sitcom for the under-fives.

Tilly is about to go global, although Dunbar’s trying not to think about that. The picture books which began life as a series of scribbles made on her kitchen table have gone on to become a hit CBeebies TV series that was recently sold to 25 international partners.

Tilly and her eclectic collection of friends will soon be beamed into households everywhere from Germany to Japan and, later this year, followed by a full range of promotional merchandise.

“Suddenly they’re not just my imaginary friends,” says Dunbar, “They belong to everyone.”

Although she has already enjoyed huge successes with her previous work – 2007’s Penguin won the Booktrust Early Years Award as well as the silver medal in the Nestle Children’s Book Prize) – Tilly is her biggest hit to date with more than 50,000 books sold in the UK and more than 150,000 internationally, according to the promotional blurb.

The books, the first of which were published in 2009, marked a fresh start for Dunbar who felt that, up until then, she had been unwittingly writing the same story over and over again.

“Before Tilly, all my books seemed to be about the lonely child struggling with a creative problem and I knew I had to do something different.”

She was living in a chaotic London house-share at the time – several friends all cooped-up in the basement of a vicarage – and that eventually proved the inspiration for this new chapter.

“It was the best of times and the worst of times,” she says with a laugh. “Our individual living areas were divided only by a curtain and, although we all loved each other, there were times when it just seemed impossible. Everyone was ‘borrowing’ each other’s things, getting in each other’s way and falling out.”

But it was just these quirks that would inform the characters in Tilly And Friends – Hector, the sensitive, giggly pig; preening Pru the chicken, Tumpty the innocent elephant, Tiptoe the rabbit and the mischievous furniture-chewing crocodile Doodle. One might assume that must make Dunbar Tilly – the little girl trying to hold everything together. She’s not so sure. “I’d say I have more in common with the crocodile,” she grins.

But there are echoes of the creative Tilly in Dunbar’s description of her childhood in Stratford-on-Avon when she pored over books by Roald Dahl, Maurice Sendak and others.

“I remember it as a very simple time. I was always making things and playing with stuff – using my imagination. Is it like that for kids now? Life seems to be much more complicated.”

Her mum Joyce is also a successful children’s writer (the pair collaborated on 2005’s Shoe Baby) and Dunbar remembers evenings entranced by her mum’s make-believe.

“It’s hard to know how much mum’s career influenced me but it certainly gave me confidence that writing was something you could make a living from.”

She began writing for herself aged 16 when she made a series of cartoon books – “Mainly about under-age drinking, since that’s what I was doing at that time!” – before starting art college at 18. She had intended to draw rather than write but found she needed a ready supply of stories to illustrate.

Now books evolve through both drawings and notes.

“I record anything I find interesting because you never find a story idea in the same place twice.”

2012’s Arthur’s Dreamboat, about a little boy who dreams of a beautiful boat that then starts to grow on his head, came about when she rediscovered a sketch she had made of a child walking on Hove beach.

“The boat was on the horizon and it looked from where I was standing as though it was on the boy’s head. I didn’t think much of it but when I came across the sketch years later the story started to unravel.

Why then, I don’t know. It’s a complete mystery to me how and why my stories come about. I wish I knew.”

Flyaway Katie was her first major success and trumpeted the arrival of an author unafraid to tackle uncomfortable subjects like feeling sad.

“I hope my books deal with complex themes but in a way children can relate to, because if it isn’t ‘real’ it just doesn’t work as a story. I tend to write for myself and the child I was and I think that’s important. If you set out trying to write ‘for children’ you end up in danger of patronising them.”

Dunbar is a firm believer in the need for “a little bit of bite” in children’s books.

“It’s the most boring thing when books are just about everyone being nice to each other.” But she’ll admit it’s been a learning curve since the days when The Long-Nose Puppets – the theatre company she formed with old friend Katherine Morton – made an entire audience of children cry with a particularly ferocious lion.

“I always thought I loved the immediacy of live performance but I wasn’t so sure after that.”

Doodle the crocodile, from Tilly And Friends, also had to be toned down.

Dunbar’s original version bit everyone and everything, behaviour that an author can’t be seen to be encouraging in young readers.

“So the crocodile now eats apples. But I do wonder what would happen if a child met a crocodile and tried to feed it an apple…”

She catches my eye mischievously and we both laugh, even though a child being eaten by a crocodile isn’t funny.

“I don’t think there’s any doubt my inner-child is alive and well,” says Dunbar. “It’s the adult I worry about.”

*Four new Tilly books are out now, published by Walker.

* Tilly And Friends is on CBeebies at 7.40am every day. Find out more about Polly Dunbar by visiting www.pollydunbar.com.