From Fraser Nelson at The Spectator:

That fits our general idea of America: a country where the richest do best while the poorest are left to hang. The figures just don’t support this. As the below chart shows, middle-earning Americans are better-off than Brits. Even lower-income Americans, those at the bottom 20 per cent, are better-off than their British counterparts. The only group actually worse-off are the bottom 5 per cent.

I recommend the rest of the piece. It’s important to remember, though, that GDP isn’t everything. This Time response piece hits on that point:

It is also a little simplistic to equate poverty with GDP, which measures business and government spending as well as individual consumer behavior. Poverty is better reflected by rates of joblessness, education level and life expectancy. The UK’s unemployment rate is 6.6%, roughlycomparable to New York (36th among the states). The UK has a 91% high school equivalent graduation rate, which would put it in the top 5 among states. And the UK’s life expectancy at birth is over 80; that would rank it among the top 10 states.