If only it was as simple as that, andy-hughes, to consider this one issue in isolation, treating all other things as being equal and then disregarding them.
But they're not all equal. For example, cutting and pasting my response from another thread ...
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Europe has loads of space to take more migrants. The problem is that the UK doesn't.
Just doing the sums based on these numbers ...
https://en.wikipedia.org/wiki/Area_and_population_of_European_countries
... you find that ...
* Germany would need to take 10 million more people to be as crowded as the UK
* Italy would need to take 17 million more people to be as crowded as the UK
* France would need to take 76 million more people to be as crowded as the UK
* Spain would need to take 83 million more people to be as crowded as the UK
In fact, the whole of Europe could take six BILLION more people before it was as crowded as the UK. There's loads of room in Europe - just not in our part of Europe.