Children's author Frances Hardinge wins Costa Book prize for The Lie Tree

Children's author Frances Hardinge has won the 2015 Costa Book of the Year for her supernatural tale The Lie Tree.

Hailed by judges as "a fantastic story", the Victorian detective novel is the first children's book to scoop the coveted prize for 14 years.

It saw off competition from debut novelist Andrew Michael Hurley's gothic horror story The Loney and esteemed author Kate Atkinson's A God In Ruins.

The last children's book to win the prestigious prize was Philip Pullman with The Amber Spyglass in 2001.

Despite entering the evening as a betting underdog, the judging panel declared The Lie Tree the winner at an event in central London, after an hour and a half of deliberating.

Judging panel chairman James Heneage said: "First and foremost, Frances Hardinge's The Lie Tree is a fantastic story.

"It is an important book, not only because it is a great narrative, with great characterisation, but because its central message of possibility for an intelligent girl who is out of touch for the age in which she lives is a very important one and, I would argue, relevant for today.

"I think lots of 14-year-old girls today would also feel they are quite often out of touch - which could be in anything from boys to motor cars to the art on the walls.

"I think this brilliantly articulates what goes in a clever 14-year-old girl's mind, particularly one who has this deep interest in science."

The Lie Tree follows the story of teenager Faith as she tries to uncover the details of her father's mysterious death.

The budding scientist finds a tree which, when fed with lies, bears fruit that acts as a gateway to understanding previously incomprehensible truths.

Her struggle for answers is set against the backdrop of a male-dominated Victorian society, where women were "seen and not heard", Mr Heneage said.

All five nominees for the best book award had already triumphed in separate Costa award categories, including first novel award, novel award, biography award, poetry award and children's book award.

The Costa Book Awards solely considers authors living in the UK and Ireland.

Hardinge was visibly surprised as she took to the stage and later said she was waiting to congratulate someone else for winning the award.

"I feel like I have fallen through a hole to another dimension that seems implausibly idyllic, but I like it here and I am staying," she said.

"I was standing there waiting to find out which of the other people had won so I could congratulate them."

The 42-year-old author, from Isleworth, west London, previously worked as a technical author and a graphic designer while writing her first novel.

The Lie Tree - her seventh book - explores the issue of gender roles, which she says often features in her stories.

"Female education is very important to me," she said. "I always have a problem with any convention, any prejudice that allows people to treat other people as inferior people.

"I don't write manifestos and then wrap a story around them, but while I am writing a story I do have a few bees in my bonnet and sometimes they come out for a little buzz."

Hardinge said it was amazing to be the first children's author since Philip Pullman to claim the prize and that she hoped it would bring children's literature into the spotlight.

"In the wider world, sometimes children's fiction is seen as a bit lightweight, in a way that I think is not deserved," she said.

"I would also see this as a recognition of the wonderful work that is being done out there throughout children's and young adults' fiction."