 But if the principal argument for immigration is that Britain needs more people, given its ageing population, the arguments against it include the strain higher numbers put on the country's already stretched public services. Here's the very briefest of rebuttals from Paul Johnson of the independent think tank, the Institute for Fiscal Studies. On average, immigrants pay more tax than they use in terms of public services. They're younger than the average for the domestic population. They use the health service less and so on.