Around the early 2000s, early in the G.W. Bush administration I believe, I saw a US theatrical release of a feature-length dystopian film set in a slightly near-future UK. I think there were dissidents/"terrorists," a train, a secret camp, a car chase, an ambush along a tree-heavy rural roadway, and a bomb, IIRC. I remember my contemporaries being a little surprised that the film could get away with its commentary on the nature of the "War on Terror," and a sentiment that the UK setting made it more acceptable to an American audience.
The main image that stuck in my mind was a dark coloured red and black billboard at a train station featuring a close-up of a Muslim woman's veiled face and some "See something, say something"-like exhortation. I think the photo may have been subtly live in the manner of the 'wanted' posters in the Harry Potter films.
Any clues as to the identity of the film? Thank you.