Just saw this movie on a movie channel over here. Posting about it because I really suggest you folks see it. It's a British thriller/horror (not boring zombies or out-of-nowhere serial killers, but instead real-life horror) movie that really gets under your skin. It's a very disturbing movie. The British cinema really is moving along the genre in leaps and bounds. More and more I'm moving towards alternative cinema and I only wished those huge resources at Hollywood where put to good use on movies this quality.
I suggest you avoid reading any spoilers for better enjoyment. It's really the only way to enjoy these type of movie. I can assure you, despite the apparent slow start and the occasional cliches, you are in for a ride you won't forget.
And that's the last I say.