A look a Europe's population helps explain why Britain and Germany are divided over the refugee crisis

A debate is raging right now across Europe about how many refugees each country should and could take, amidst the biggest global displacement crisis in over two decades.

A particular schism has emerged between Britain and Germany.

Germany, and its ally France, are speaking about the crisis in "moral" terms and committing to taking thousands of refugees.

Germany Chancellor has become a figurehead for the crisis in Europe and has championed rehoming quotas for countries, which are set to be unveiled next Wednesday (the UK is not taking part.)

Britain meanwhile has resisted taking in any more refugees, with David Cameron only relenting to taking in 20,000 Syrian refugees over 5 years under serious public and political pressure.

Much of the argument about why Britain shouldn't commit to taking large numbers of refugees has centred around the cost. But several commentators are now starting to point out that the real argument, and the real difference between Britain and Germany, is about demographics.

Germany could do with an influx of young migrants to supplement its ageing workforce, while Britain is less in need.

The BBC's Robert Peston pointed this out in a blog post on Monday:

The two relevant points (leaving aside moral ones) are that:

1. the UK's population is rising fast, whereas Germany's is falling fast;
2. the dependency ratio (the proportion of expensive older people in the population relative to able-bodied, tax-generating workers) is rising much quicker in Germany than in the UK.

The European Commission's Ageing Report, published earlier this year, included a graph that shows the projected change in labour supply between 2013 and 2060 for different counties. The UK's workforce is forecast to grow, while Germany's is expected to shrink.

By 2060, Germany's current population of 81 million is projected to fall to 71 million, while the UK, a vastly smaller land mass, will overtake it to become the most populous EU nation, rising from its current 64 million to 80 million.

The dependency ratio in Germany - the ratio of pensioner to working age people whose taxes support them - is set to rise to 59%. That means the taxes of roughly more than 1 working German will have to support 2 retired Germans.

For Germany then it makes economic sense to take in refugees, a transfusion of young workers whose taxes can help support its ageing population. Tory MP Boris Johnson highlighted this in his column for the Telegraph this week, saying:

It is certainly true that over the last few years, Germany, Italy and several other western European countries have seen a marked fall in their indigenous birth rate. They have ageing populations, and are failing to produce enough young people of their own. In accepting large numbers of energetic young migrants, they are actuated not just by compassion - though that cannot be denied - but also by a certain economic logic. It cannot be said Britain is in exactly the same position. We are going through a population boom. Our schools are bursting - certainly in London - and the demand is rising the whole time. The population of the capital went up by about 122,000 last year alone.

From a demographic point of view then, it perhaps makes less sense for the UK to take in refugees in the same numbers as the UK.

This argument also casts some doubt on German Chancellor Angela Merkel's moral positioning - why so keen to help refugees from the Middle East but unwilling to aid Greece, where people are being driven to suicide by German-mandated austerity?

But this is just one aspect of the debate - whether it is a moral duty, as France and Germany argue, is another matter.