Alternate title: Death Wish in Old Blighty. Starring Michael Caine as Charles Bronson and Emily Mortimer as Vincent Gardenia. Sorry to give away almost the entire plot, but it's still pretty good.
Mr. Caine plays the title character, Harry Brown. He lives, roughly, in the worst place in England, called "the Estate": a huge beehive public housing development that is continuously terrorized by Roving Bands of Youths Committing Random Acts of Violence (WBAGNFARB). The cops are ineffectual against them.
God has also been unkind to Harry: his young daughter died years back, and, as the movie opens, his cancer-stricken wife is circling the drain in the local hospital. Worse, his best friend and fellow-geezer, Len, has been targeted for harrassment by a local gang; Len tries to retaliate on his own, but it doesn't work out well.
This is the last straw for Harry, and he has nothing to lose. (Well, except his life, but that's OK with him.) He's no Bruce Willis superman, but he is an ex-Royal Marine. He may have lost a step or two, but he hasn't forgotten much. He's seriously bad news for the bad guys.
The movie is very violent, but even more shocking is the utter Hobbesian degeneration of the "Estate". We note, but are not beaten over the head with, the antiseptic tidiness of the police offices contrasting with the filth and anarchy outside; the commander is a self-aggrandizing and effete fool. Emily Mortimer is (apparently) the only cop who really cares about fighting crime, or has any compassion for crime victims.
[Libertarian side note: According to the IMDB, the movie was filmed at Aylesbury Estate in South East London, and Wikipedia notes that it is "often used as a typical example of urban decay." Unsurprisingly, it's also a typical example of failed social engineering making the people it was designed to help much, much worse off.]