Meg Rosoff’s teenage love story set in a contemporary Britain at war, How I Live Now, has appeared on so many award shortlists this year that it is easy to forget she is a first-time author.

Now she has won an award for that, too. Last night the former advertising copywriter received the Branford Boase Award for the most outstanding children’s book of the year from a new writer.

She had just returned from Chicago, where she collected the American Library Association’s Michael L Printz Award “for a book that exemplifies literary excellence in young adult literature”. How I Live Now has also won the Guardian Children’s Fiction Prize and been shortlisted for the Whitbread Children’s Book of the Year award, the Orange Prize for new writing and the Booktrust Teenage Prize, to be awarded in November (TES, June 10).

In memory of the late children’s writer Henrietta Branford, and her editor Wendy Boase, editorial director of Walker Books (both died in 1999), the award is shared with the winning author’s editor, this time Rebecca McNally, of Penguin Children’s Books.

Ms Rosoff took two months’ unpaid leave from work in 2001 to find out if she could write a novel. She wrote a pony book, which she has decided not to publish, and a picture book, Meet the Wild Boars, which was recently published in the US and will be available here later this year.

With TV images of the Bosnian war in her head, she wanted to write a story about a family living under occupation that would show “that war is not something ‘over there’.”

How I Live Now embraces a bundle of children’s-book conventions and turns them on their head. When world-weary Manhattanite Daisy arrives to stay with her eccentric English cousins, she is dragging baggage familiar from teenage novels: angry at her father and new stepmother, she has developed anorexia.

She is embraced by her Bohemian, chaotic, practically-minded family in their sprawling farmhouse (“The sort of family I loved to read about, nothing like mine,” says Ms Rosoff, who grew up in the suburbs of Boston) and the author swiftly dismisses the one remaining adult, Daisy’s Aunt Penn.

Daisy’s passionate sexual relationship with her 14-year-old cousin Edmond is a brief diversion before we learn, slowly and plausibly, that England has been invaded, food runs out and health services collapse.

Daisy and her nine-year-old girl cousin Piper are billeted separately from the boys. Daisy’s struggle to reunite the family, her perilous cross-country journey with Piper and their encounters with violent death and near-starvation bring the reality of war “over here”.

When they have to live off the land, it is for real, and Daisy’s anorexia is eclipsed by real fear for her survival. Meanwhile Aunt Penn, who has gone away to work on “the peace process”, never comes home.

* geraldine.brennan@tes.co.uk

How I Live Now is published in paperback by Penguin this week. For details of the annual BBA competition for young writers, see www.branfordboaseaward.org.uk