Michael Caine saw a lot of himself in the character of Harry Brown, e.g. they're both combat veterans (Harry is a Marine who served in Northern Ireland, Caine served in the British Army during the Korean war), and Caine lived in the same area that Brown does. It was things like these that drew him to the film.
During the riot scene, a Volvo hatchback is torched using a petrol bomb. Later in the sequence the car is seen again, and the fire has gone out. It is possible, although unlikely, that the petrol did not ignite the interior (accelerants in isolation do not burn for long), but the car body shows no oxidation or paint damage, even around the roof.
Although supposedly set in south London, most of the graffiti on the estate has been lifted straight from the New York underground scene by the movies art department, with internationally recognized American Graffiti artists such as 'Kez' and 'Skuf' and 'YKK crew' adorning the supposedly British sink estate.
Harry Brown: I don't reckon you've got long. Seen that before. Gut wound. The slug's probably torn right through your liver. Mate of mine in Ulster got caught in sniper fire. Bullet blew his inside out. He screamed for a good 10 minutes. We couldn't send a medic in, the section was too hot. So we all took cover... and watched him die. I've never told that... to anyone... you should've called an ambulance... for the girl...