Saoirse Ronan is set to star in 'How I Live Now'.

The Irish actress will take on the lead role in the Kevin Macdonald-directed movie adapted from the Meg Roskoff novel, about a troublesome girl named Daisy from New York who is sent to a remote farm in England in the near future to stay with her cousins and aunt.

While she quickly adapts to life in the countryside, and finds romance, she and her cousin Piper are forced to survive alone in the woods when a world war breaks out, the children are separated by soldiers and her aunt becomes stranded in Norway.

Jeremy Brock and Tony Grisoni have adapted the book - which was published in 2006 and won The Guardian children's fiction prize - for the big screen.

Before starting work on 'How I Live Now' Saoirse will film 'The Host', based on the novel by 'Twilight' scribe Stephenie Meyer but recently admitted she has no idea how it will be filmed.

The 17-year-old actress will take on the lead role in the movie about an alien race called Souls who take over Earth and its inhabitants but admitted filming her role - which will see a Soul named Wanderer and a human, Melanie vie for the same body- will be a challenge.

She explained: "We're doing 'The Host' at the start of next year. We're figuring out how to film it at the moment. Andrew Niccol the director knows what he's doing, I think it seems incredibly challenging but he knows exactly what to do so I feel very safe."