To shape a film in an (correct) dramatic way you need (much) more than just a realistic story/plot . Basically there has to be a believable setting - in this case a city which portrays/stands for football and hooliganism. The coice of London wasn´t random.On the one hand, England is not only known as the mother country of football, but also as the source of hooliganism. But on the other hand even a city like London, the capital city of the british kingdom, has to deal with the same problems as every other city: Ghettoization, gang-culture and street violence. These circumstances predestined London as the place of the storyline/story.