London is safe enough, and the food should certainly not be knocked, but there is no way it London could handle that number of visitors. From hotels to transportation to crowd control, it just wouldn't work. Paris takes it easily.
I'm not sure - london seems to be a lot less safe than it was 5 or 10 years ago, and they have the issues of sports hooligans and binge drinking. don't get me wrong, I love london, but it isn't the type of city I would want to bring tens of thousands of forigners to. f, I was in Paris during the world cup, and the city worked very well, the crowds were handled pretty well, I think.