No matter how reliable a borrower a government might be, at a certain point debts run up with a larger population become impossible to service with a smaller one. The natural response for policymakers is to simply wave a hand and say that we can deal with this problem through higher levels of immigration. If people won’t have children, we’ll simply import the workers we need.
And from an economic perspective, this is tempting: you don’t have to raise taxes, you don’t face a bond market crunch and firms have a plentiful labour supply. Indeed, it’s hard not to think that this logic has played a role in the unwillingness of recent British governments to reduce the numbers arriving.
For all that people like to vote against immigration, the line goes, they like to vote for entitlements – for free healthcare, benefits and pensions – enough that the grumbling can be disregarded.
But it’s not clear how far this logic can be pushed. As Paul Morland, a demographer, has noted, if we tried to maintain our ratio of elderly to working age population, we would see the share of the population born overseas rise each year. By the 2080s, it would pass 37pc. And if the birth rate continues to fall, it would pass 50pc. Once you go down this path, you have to keep bringing in larger cohorts.