If there's one lesson Jill Murphy learned when she was a teen, it was to never give up.

Now 66, she started making miniature books aged six and wrote her iconic tale, The Worst Witch, when she was just 18 - but had several rejections from publishers.

"They said children would be frightened about a school for witches - they got that one wrong, didn't they?" she says with a wry smile.

"This was a very long time ago, I might add, way before any other books about schools for witches, so I'm very proud of it, it was a very good idea."

Not that Murphy is bitter about that concept cropping up again, in other writers' works...

"I'm very happy for everybody, there's plenty of room for all of us... People draw their own conclusions. But with that one, it was the best idea I ever had," she says, grey eyes twinkling.

She clearly recalls the inspiration behind it... Murphy was "an ordinary little girl" growing up in Chessington, Surrey, who'd won a scholarship to a grammar school. One evening, she'd invited some friends home for tea.

"It rained on the way home and my mum answered the door to us and we were absolutely like drowned rats, and my mum said, 'Look at you three, you look like three witches standing there' - and that was my light bulb moment. I thought, 'school for witches'," she recalls.

"I wrote it, sent it off to three publishers and they said it would frighten children, so I put it in a drawer, and didn't take it out again for another three years.

"I had one last try, which just goes to show you should never give up, with a very small publishers. I had this manuscript and some drawings, and it went off like a rocket."

The Worst Witch was first published in 1974 - but Murphy had fairly modest ambitions.

"I come from a time where girls weren't really expected to have careers. I just wanted to get married and do the ironing and live down the road from my mum. I hadn't thought in terms of a career, it was just something I could do.

"The only reason I wanted to have it published was because I wanted to have a book between The Lion, The Witch And The Wardrobe and The Secret Garden with my name on the spine, and then I could put them all together on my bookshelf and feel clever! I never thought any further than that."

Now, more than 40 years later, Murphy is working on the drawings and words for her eighth and final book featuring Mildred Hubble and co.

"Mildred is completely me, at the convent school where I didn't do very well and I was absolutely desperate to be like everybody else," she says. "She looks like I did, I was tall and thin, with long dark hair. Virgin Mary was always blonde, so I fancied doing a story about a heroine with dark hair, who was tall and scrawny."

There have been several TV adaptations of the books, with the latest one "in the pipeline", and Murphy won't be closing the book on The Worst Witch entirely after the eighth one is published; she's already started drawings for a book for younger children about Mildred's not-black cat, Tabby.

"I'm longing to do the pictures. I've done one of Tabby when it's a really little kitten, and you can tell which one's Ethel's, because it's mean-looking. Children often write to tell me Tabby's their favourite character, so I think I might do three books."

She's also just finished another picture book, called Meltdown, about a baby rabbit kicking off in a supermarket.

It's the latest dose of animal magic from the creative mind behind the 'Large Family' of elephants, who first appeared in Five Minutes' Peace back in 1986. And it's based on an experience she had as a single mum to son Charlie, when he was just a toddler.

"He went totally berserk about a cake in a supermarket and I was being really feeble, saying, 'Just hold the cake', and then he went, 'I want to eat the cake', and ripped the box open and the whole thing fell out and he was just stuffing pieces of it in," she explains.

"I fought him over the cake and then he went rigid in the trolley when I tried to get him out, so that's one of the illustrations, when the mum's trying to get Ruby out of the trolley and she's lifting the trolley with it."

Murphy's books are all based in reality, including Five Minutes' Peace, which turns 30 next year.

Before she became a full-time author-illustrator and mum, Murphy worked as a nanny and in a children's home, and used to help out her best friend, who was married to a busy doctor with three children.

One evening, she arrived just as her pregnant friend was about to take a bath, and was invited to sit on the floor for a natter. "She rested her teacup on the bump and I remember thinking it would make such a nice drawing."

Murphy then watched with amazement as her friend's children traipsed into the bathroom in turn demanding their mother's attention - she wrote it all down, and the book was born.

She became a mother herself to Charlie at 41, after a miscarriage and marriage break-up left her fearing she'd never have kids.

"I was absolutely delirious when I had him, I didn't think I was going to have any, my husband had left.

"It was quite a tricky birth and everybody felt so sorry for me, because I was on my own," she continues - pointing out that she had "so much help" and "could just snuggle up with the baby, which was lovely".

"I used to take him everywhere. He was the most darling little boy, and then he was a horrendous adolescent, like they are, it's very much like the young stag lowering his antlers and I was the only one there," she adds of Charlie, now 25, who overcame dyslexia to get an English degree.

Murphy was diagnosed with breast cancer when Charlie was five.

"That was terrifying, because your first thought is, 'He won't know you if anything happens to you'.

"First of all you start making bargains, you think, 'Can I just have five years to see him through to 10?' And then you think, 'Could I get him through to 15?' - and then you start thinking, 'Can I just last forever now? Thank you very much'."

When he was nine, they moved down to Cornwall so Charlie could enjoy a childhood that involved being able to go surfing after school. "It's the most wonderful place in the world to live," Murphy says today.

"My morning routine, before I start my writing, is to go and walk along the beach, take my bearded collie puppy across on the ferry to Padstow and have a nice breakfast at this lovely little cafe where they're very nice to dogs," she reveals.

"It's like a natural high, I'm almost floating around."

:: Jill Murphy was guest judge for the Virgin Christmas Train design competition in partnership with Book Trust. The winning design will be unveiled on December 1

:: Five Minutes Peace: 30th Anniversary Editions in hardback and board book formats by Jill Murphy are published by Walker Books, priced £9.99 and £5.99. Available now