I'm not an author or anything but I live in London, and not the fun part, and I think there maybe cause to add more phonetic spelling of your character's dialogue. If, for example, the story takes place in the UK you can assume that everyone understands each other and throw in the occasional 'nuffink' or 'bruv' for colour. However, if it takes place in most places in North America no one is likely to understand him anyway and confusing your readers, a little, maybe appropriate.
By the By... do you really think Tim Roth has a thick accent?