Bear in mind that obviously the mean salary in London is going to be far higher than the median (the finance industry will skew it), while I'm not sure that's as extreme as Mississippi. Additionally median salaries reflect a lot of service jobs and similar labour. Dubai has a lower median wage than either London or Mississippi, but people don't think of it as economically broken.
Comparing California (an extremely large state that I presume has cheaper housing outside major urban areas) to a city seems a bit of a poor comparison.
I don't disagree that the UK has high energy costs.