Not sure if this question can be answered but I've always been intrigued as to what the population density would look like if people returned to the country of thier birth. What would the most populous country be for example?

In a news story this this morning I noticed that the UK population is growing at its fastest rate since 1973, a period of severe economic distress. Is there any evidence or studies that show that there is a relationship?

The usual explanation I see is that people stay in more during a recession, but this seems over simplistic.

I wondered if there was maybe a feedback/tipping point effect, so that once a certain percentage of people are expecting, there is suddenly a rapid increase; or if the population reacts as a whole in periods of distress by increasing birth rates?