I found a source that prices

[(former)FormerSanDiegan]

I found a source that prices per capita income in both dollars and purchasing power (to try to account for the effect that PD points out).

In both cases the US per capita income is higher than the UK.

Per capita income (US$)
US: 43,560
UK: 37,740

Adjusted for purchasing power
US: 42,000
UK: 33,960

SOURCE:
http://siteresources.worldbank.org/DATASTATISTICS/Resources/GNIPC.pdf

So, the first point is that incomes are actually nominally higher in the US (not lower) AND purchasing power extends that further.

A previous post showed UK median income as higher than the US. How is the median higher than the per capita income ? Please provide a source. If the median is indeed higher it means that there must be much fewer people in the workforce in the UK as a percentage of the population than in the US.
Fewer % of workers pulling the weight means more social programmes, and the associated higher tax burden.