Research newly published lists the most overpopulated countries. When we talk about "overpopulation" (as opposed to population size), we are referring to the link between the human population and its environment. Therefore, it's not just the size or density of the population that matters, but how that population relates to sustainable resources.
The Overpopulation Index  is thought to be the first to rank countries by these criteria -- looking at how dependent they are on other countries, and whether they consume more than they produce.
Here's the top ten:
According to these figures, the world as a whole is overpopulated by two billion. The geographical location of countries deemed overpopulated is interesting -- there are nine Middle Eastern countries in the top 20, and eight European. Despite popular perceptions of China and India, these countries come in much lower, at 29th and 33rd, respectively. This shows, again, that population size or density is not the key measure.
The UK comes in at a slightly less respectable 17th. Its self-sufficiency rating is 25.8 per cent, meaning that Britain could only support a quarter of its population -- about 15 million -- if it had to rely on its own resources.
It's worth noting at this point that overpopulation is a hotly contested issue. The index was compiled by the Optimum Population Trust, which advocates a voluntary "stop at two" policy on children in the UK, and has lobbied for stricter controls on immigration , saying that "immigration has brought no overall benefit to the UK". I won't get into these debates here -- you can read Philippe Legrain's excellent critique  of the "Britain is full up" argument if you want the other side of the story on that particular point.
The key point here is sustainability. Even if population growth were to level off in the UK, we would still, by these measures, be unable to support ourselves unless the population shrank drastically, or food production grew. A situation where all imports disintegrate is unlikely, but improving food sustainability  can only be a good thing.