Before Alex Comfort became famous for The Joy of Sex, he was a plain old gerontologist and for the Observer Magazine of 23 September 1973, he wrote about the science of ageing (‘So you want to live longer’).

‘People are living longer on average,’ he wrote, ‘but at the same time the “lifespan” of man is almost the same as it was in the time of Moses… three score and 10 to four score years: 70 to 80.’ Comfort admitted that ‘We do not yet know how ageing works. We do know that it can be modified, and probably slowed – at least in rats and mice.’

He showed a fondness for an explosive metaphor: ‘There are several places where the gerontological bomb-disposal squad would naturally make their first search for the time-clock… We have to look at various slow processes of hardening, perishing or sludge accumulation in the non-cellular parts of the organism.’ Not an easy task, although Comfort believed the Americans were probably the ones most likely to succeed.

‘The best way of ensuring long life,’ he said, ‘is by vocal pressure on the United States Congress. The US is the country with the biggest investment in gerontology today.’

There were some lovely interviews with centenarians, including Richard Southey, 108: ‘His greatest pleasure today is his pipe, a habit that he has pursued without let-up since, he insists, he was nine, when he started work driving ponies in the pits at Denaby, Yorkshire.’

And then there were the celebrities who were asked if they’d like to reach 100. Roger Moore, 44 (he reached 89), said he was happy to do so as long as he was a burden on the state, but not his children (spoken like a true tax exile). Barbara Cartland, 69 (who died at 98), said: ‘My first reaction is No!’ but then quickly remembered her usual advice to neck hundreds of ‘natural vitamins’, and relented.