“Don’t abandon. Never go back. Write the same amount every day. Put down a sentence and see where it takes you.” #BathKidsLitFest Day 9

It’s another great night at the The Telegraph Bath Children’s Literary Festival thanks to the appearance of Andy Mulligan (author of Ribblestrop, Trash, and The Boy with Two Heads, amongst others) and John Boyne (whose novels for children include The Boy in the Striped Pyjamas, Noah Barleywater Runs Away and Stay Where You Are and Then Leave), brandishing books so hot-off-the-press they’re practically smoking.

Both Mulligan and Boyne had careers before they turned to writing full-time: Mulligan worked in the theatre for about a decade, “very unsuccessfully” before being made redundant “thank goodness!” while Boyne spent seven years at Waterstone’s in Dublin.

The aggressive boys’ grammar school in London that Mulligan attended when young – “a place of extraordinary cruelty” he muses ruefully – informs his fiction, if not consciously. He’s interested in psychological torment and friction between characters, but also the enduring power of deep friendships. Next week, for the first time, he’s going back to his old school. “You might come across the very toilet your head was thrust down,” offers John McLay, artistic co-director of the Festival, who’s in the red chair tonight.

Boyne also had a fairly miserable time of it at school and his experiences fuelled the writing of A History of Loneliness, an adult novel. He was an avid reader as a child, taking out three books a week from his local library. Like many writers, he’s a book fetishist, loving the paper, the typeface, the physical handling of a book in printed form. Put him in a stationery shop and he’s in heaven.

For Mulligan, the works of Enid Blyton were a childhood delight. “Mallory Towers was beautiful,” he says wistfully. But he still recalls the moment of realising that no member of the Famous Five ever got hurt when deep in adventure, and then he just sort of lost faith. “Their life was too sunny. I wanted menace.” It wasn’t until he read Marianne Dreams by Catherine Storr (published in 1958) that he got what he’d been thirsting for.

Boyne has some good advice for aspiring writers: “Don’t abandon. Never go back. Write the same amount every day. Put down a sentence and see where it takes you.” Mulligan seconds that, adding that, ”Writing a book is a marathon. The best advice I was ever given is to just finish it. Even if it’s no good, you’ll have the experience of shaping something.”

And so to their latest novels: Mulligan’s Liquidator is a thriller that has an addictive energy drink, a clumsy 14-year-old doing some work experience, and Machiavellian corporate shenanigans at its heart. Boyne’s The Boy at the Top of the Mountain follows the orphaned Pierrot from Paris to Germany in 1935 and imminent war. The house where Pierrot ends up is no less than the Berghof, the home of Adolf Hitler.

Why write, asks McLay. “I really couldn’t do anything else,” answers Boyne. “It’s part of my psychology.” And for Mulligan? “The pleasure. It was my hobby. It remains my hobby.”

And what next? Boyne’s on the second draft of a book set in Ireland, spanning 70 years. And Mulligan is writing a book about a dog with an identity crisis who just wants to be a cat.

Claudia Pugh -Thomas was at Writing YA: John Boyne and Andy Mulligan at  The Telegraph Bath Children’s Literature Festival 2015