I think people who nitpick about things like "I saw a guy walking to work way off in the distance there" and "There was no blood and cars and dead people all over the streets etc." REALLY missed the point. I can't immagine it was easy to get the streets and express way emptied long enough to shoot a scene that comes accross as eerie and devestating let alone spread blood and cars and extras posing as corpses etc.
It's a MOVIE you know? What do you expect? They can't ACTUALLY have london evacuated and I'm sure Manchester wasn't REALLY on fire you know...NONE of that stuff was real...the point is that it was FREAKY AS HELL! The THOUGHT alone is messed up and to actually get a glimps of it was AWESOME! Yes there are flaws when filming a scene that requires an entire city to be empty, but I think they pulled it off superbly!