Why are the poorest regions in the UK the poorest regions in Northern Europe?

[Posted by Prof Henry G. Overman] A few weeks ago the map below showed up in my twitter stream. It had been retweeted hundreds of times. At the time, I meant to write a post on the numbers behind the map. In particular, I wanted to take issue with what it tells us. According to the side bar: "The poorest UK regions are by far the poorest in Northern Europe. This is because the UK is much more unequal than all other countries, where there is nowhere as rich as London, but nowhere as poor as our poorest neighbours"