London is the main place where the game is taking place.
What's happening in LondonEdit
We know very little about what has really happened and still is happening in London, but all we know is that the London is somehow quarantined.
In the newspaper media somehow, there are titles stating many things, some of them are:
"London Nuked" and "Search for Survivors Continues", if you listen to the titles it seems like the Aliens invaded London and killed so many people, ruined what they could and just destroyed so much to such grade that finding a human alive now in London is harder than anything else at the moment.