True, England isn't a country by itself, hasn't been since 1707, Britain is the country, of which England is the largest part, and in which most people live.
But this is about the population densities of countries. Not regions. The fact that the stat excludes Wales Scotland and Northern Ireland is very significant because it ignores quite a lot of land. Thus the population density of the country is likely much lower.
It also means that England is not a fair comparison with the Netherlands, or Germany. Which is exactly what the article does.
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I know Wiki is dodgy, but it'll do for now. The most recent I could find was the estimate for 2005 (cited as being from the UN World Prospects Report), which has the UK as 244/sq km
Another NationMaster table which is more up-to-date (a target='_blank' href="
)" target="_blank"rel="nofollow">http://www.nationmaster.com/time.php?stat=geo_ pop_den_peo_per_sq_km&country=uk#source">he re) has the UK as a whole at 248/sq km in 2005.
I know there's still a three-year gap but it does show you how much difference there is between England and the UK - so to focus on the England stat is frankly just scaremongering.