It's not easy to make a film about children being taken from their parents - especially a true story. You either stick to the facts for a straight TV documentary, or you go the full-on emotional route and end up with Changeling. Jim Loach (son of Ken) goes down the middle, working with an understated script and wisely avoiding any connection between Angelina Jolie and children. Because that's the kind of topical joke people still make in 2011.

Margaret Humphreys (Watson) is a social worker. She's from Nottingham, a place where nothing happens. So when a young Australian approaches her in the street, claiming to have been shipped out of the country when she was four, Margaret does the polite thing and ignores her.

A little research later and she unearths a mass child deportation scheme from the UK to Down Under that went on for years. Told they were orphans and promised oranges and sunshine, the children arrived to find a life of loneliness and labour. And no oranges. With both governments turning a blind eye, Margaret takes on the job of victim support herself.

This being a film, it only takes her 10 minutes to pair up the first woman with her long lost mum. Five minutes later, she's at a picnic on the other side of the world, people queuing up to tell her their stories. It's never about Margaret's home life (Loach dodges any cliched family arguments), the film focussing on people like Jack (Weaving), a bloke with a great big bushy beard and a whole load of angst.

Searching for an identity in his horrible past, Hugo Weaving spends most of the movie mumbling and crying - and does it very well. He's a great contrast to the harsh and detached Len (an unrecognisable David Wenham), who spent his childhood being exploited by the shady Christian Brothers movement.

At the heart of it all is Emily Watson, anchoring the film with an emotional performance that doesn't break through the surface, even when she starts receiving death threats. Thanks to her restraint, Watson sells lines like "I don't know about the man in front of me but I'd like to speak to the boy inside" without sounding contrived. She even makes admin montages believable.

Watson's the perfect match for Loach's matter-of-fact tone. He almost doesn't direct at all, letting locations announce themselves and leaving actors to fill out the frame. One moment sees Weaving break down close to the camera with a calm beach stretching out in the background. It's a low-key and effective approach.

Ultimately, Rona Munro's screenplay is too committed to the history books to find a full sense of closure - Gordon Brown apologised for the events as recently as 2010 - but the open-ended conclusion gives Oranges and Sunshine a raw, relevant edge. It's either that or get Angelina Jolie on board. And nobody wants that. Think of the children.

VERDICT

A calm, moving debut for Ken Loach Jr, Oranges and Sunshine is simply told and shockingly accurate.