They have gone for a look very reminiscent of the posters for German Expressionist movies of the Twenties and early Thirties. The choice is probably deliberate as the Expressionism movement preceded the rise of Fascism in Germany and thus echoes the background of the events in the movie which takes place in a dystopian future Britain that has become a totalitarian state.
The four posters can be viewed at the following urls
Poster 1
Poster 2
Poster 3
Poster 4
I think the second one is my favourite.
