I disagree with regard to Eastern European part. Most of the emigration was unskilled labor. They were not below poverty line, they could organize move to UK, but they were never middle class in Poland, etc, and they usually aren't middle class in the UK. The second batch of emigrants is graduates entering the job market sometimes with degrees irrelevant in current market. So they decide to start their career in another country, because they don't have much to lose. In another country they focus on climbing up, often in a career not related to their education or previous aspiration.

The doctors, etc are a minority. A visible minority, because their move harms their country of origin more than a loss of a builder from a social perspective but still a minority.