The Weatherman by Royston Reeves

Will's a nice guy. So when he takes a shortcut to the tube station after a few beers with his mates from work, he steps out of the way of the fellow who's staggering towards him. But he-deliberately-moves back into his path. They knock each other as they pass. Moments later, one man is dead and another's life is changed forever. Or is it? There are no CCTV cameras. There was no one else in the out-of-the-way alley. Maybe the world doesn't have to end for Will after all. But there's always someone watching, and Will's life is about to implode.