No political party will address the most immediate threat to our prosperity, though it stands in plain sight, huge and menacing. The proportion of workers to pensioners in our population is about to become unsustainable. We could tackle the problem in various ways. We could raise the retirement age and impose a haircut on public-sector pension schemes. We could make deep cuts elsewhere. We could import millions of workers. Or we could have more babies. In practice, we will probably end up...