I've lived in both London and NYC. NYC feels more diverse simply because it's a bit strange to have loads of foreigners in the country when we know very well that it's very difficult to enter the country legally, whereas London is about 50/50 british to non-british. Not to mention, GB is comprised of England, Wales, Scotland, so you have that combined with the Aussies, Kiwis, Saffers, Italians, Germans, Irish, Spanish, Russians, etc. Not a day goes by that I'm working with a non-British citizen in London. Couldn't say the same for NYC.