An 11-year-old girl, laden down with shopping bags, wearily lets herself into her house with a key. Her neighbour stops her to complain about her father’s outrageous behaviour and she apologises.

“I couldn’t get that scene out of my head and whenever that happens, I know I am on to something,” explained Oxford-based author Simon Mason. “This schoolgirl, Martha, is thrust into the parental role because her father has regressed.

“But it was the role reversal that interested me as a writer. I didn’t come at it from an ‘issues’ point of view,” he added.

That exact scene did not make it into the final draft of his new novel for young readers Moon Pie but the idea and the character of Martha remain central.

While researching the subject of young carers, he was shocked to discover how many children are in Martha’s position.

“There are a huge number of young people as young as seven who have an incredible burden placed upon them.” Despite the serious subject matter, the book is full of warmth and humour, often of the laugh-out-loud variety, skilfully intertwined with moments of sheer poignancy.

Aimed at 9-12-year-olds, it follows the story of Martha, her alcoholic father and younger brother as they struggle to come to terms with the death of Martha’s mother.

Simon Mason is best known for his popular series of four children’s books The Quigleys, which feature a fairly ordinary family of a mum, dad and two children.

In 2002, when he was writing the series, he was working for a publishing company in London. “It was an absolute nightmare. I was commuting by train five days a week and it used to take two or three hours some days. I wrote on the train, standing up.

“Once I locked myself in the toilet just to be able to sit down and write. It’s hard writing while standing up.”

Born in Sheffield, he made it to Lady Margaret Hall to study English but did not enjoy his time there much. “It was more about me than the place. I was full of adolescent angst. I’d been to an ordinary comp in Sheffield and never even met anyone from a private school before.”

He met his wife Eluned at Oxford University Press, when they both acted in the company Christmas pantomime.

“I was in the lead role but couldn’t dance to save my life,” he recalled.

Eluned was a talented ballerina who had been offered a place with the Ballet Rambert but turned it down in favour of a chemistry degree. She agreed to give him dance lessons, during which they fell for each other and went on to marry and have two children, Eleri, 16 and Gwilym, 18.

Eluned swapped educational publishing for education and now teaches science at Matthew Arnold secondary school in Cumnor.

Mr Mason is keen to emphasise that life at their family home near Abingdon Road in Oxford is normal and reasonably sane.

“Because the Quigleys were so closely associated with us, I got a bit fed up when reviewers kept describing them as ‘hapless parents. And my wife was a bit fed up that the mum in the Quigleys is always tired.”

He says his children are very good critics and he sometimes reads his manuscripts aloud to gauge their reaction.

“There is no beating about the bush. They say ‘Not funny’, ‘More jokes’ or shout ‘Boring’.

The Quigleys books have received much critical acclaim, including being nominated for the Branford Boase awards in 2003.

Other reactions have resulted in moments of head-scratching for their author.

“One teacher said the book contained blasphemy because a character used the phrase ‘Christ Almighty’,” he said.

“And in America, they were horrified at one scene in the novel where it is the mum’s birthday and the children mix her an alcoholic cocktail,” he added.

Part of Mr Mason’s week is spent as a children’s book editor at Oxford-based publishers David Fickling Books and the rest writing at home.

David Fickling is based in Beaumont Street, where there are a lot of dental practices and the author says that sometimes they can hear drilling.

Then he looks thoughtful and I wonder if he is picturing a scene for a future book about a crazed dentist wielding a drill. I can’t wait to read that one.

* Moon Pie is published by David Fickling Books at £10.99.