To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.

While many nations have aging populations, Japan’s demographic crisis is truly dire, with forecasts showing that 40 percent of the population will be 65 and over by 2055.

The report forecasts the biggest rises in London and Birmingham, with 45 per cent of the cities' population affected, up from the current 25 per cent.