How long can human beings live, anyway? It is — no pun intended — an age-old question. But the answer has posed acute challenges for governments in recent years. Sharp extensions in longevity are straining social safety nets that were created to allow the old and frail to live their last days in dignity. The probable length of human life comes with a very specific price tag.

It was not ever thus. In the early years following the Enlightenment in the 17th century, people asked why we no longer live to the age of the sages as described in the Bible, according to David Boyd Haycock, a professor of medical history at Oxford university. Adam, after all, lived to be 930 while Methuselah topped him at 939 years. Only the advent of mortality tables in the 18th century limited the debate.

The question has been given renewed impetus by a series of recent studies suggesting that the rapid pace of improvement in British longevity is now slowing. The Continuous Mortality Investigations group, which produces longevity projections based on the experience of insured and pensioned lives, found that longevity for men at age 65 fell by six months to 22.2 years while that of women fell by eight months to 24.1 years. While longevity is still expected to be higher than it is today, it is by a smaller margin than earlier forecasts. PwC, the professional services firm, recently produced a study concluding that as much as ￡310bn could be wiped from the liabilities of UK defined benefit schemes. Although a respected group of actuaries hit back, describing the assumption as “extreme”, the entire debate has escalated to the political arena.