I'm mildly surprised that it hasn't been any worse here. Even now, it is mainly a problem of the outer East and outer West of the city and the East End. Where most people live most closely to each other, in fact.
But large parts of the city are around the national average and some are a good bit better. I can't speak for anywhere else, but people HAVE significantly changed their behaviour here. We are not going out as much, hardly anyone is commuting, the Tube is pretty empty outside of peak hours. The trains are just pretty empty full stop.
Like it or not, it is still the epicentre of the nation's wealth and its economic engine. I don't blame them for hesitating about changing the Tier ; with all due respect, the impact of a change here is far more significant economically than what you do in a Northern seaside resort, in the middle of winter. There is a balance to be struck, and not only is it not easy, there is no single, definitive right answer.