Whenever I hear the phrase ‘hard-working families’ a little voice in my head asks ‘what about the lazier, chilled-out families? Shouldn’t we think about them too?’ If Cameron simply abandoned this Stakhanovite fetish and announced Britain’s move to a four-day working week, he could win the election outright.

It may take decades, but the work week is due for a rethink. It is hopelessly restrictive. Given the attacks on zero-hours contracts, you may be astonished to hear that over 80 per cent of employees on such contracts actually like them. I suspect many are people — carers, parents, students, the semi-retired — who can only work if they can work flexible hours.

Surprisingly people are often more productive when they work fewer hours. In reality, over-energetic people are often a bit of a curse (if you’ve ever worked with the worst kind of American, you’ll know what I mean). Just as highly intelligent people tend to overcomplicate things to give themselves an edge, the energetic make things more effortful than necessary to play to their comparative strength: it lets them neutralise more capable or reasonable people who can’t be bothered to play that game.

An analogy can be seen in sport. For a long time there was a class of sporting heroes who were, to put it politely, a bit porky. Ferenc Puskás and Babe Ruth weren’t slim (it was said the Babe aimed to score home runs so he could jog around the bases without breaking a sweat). The Brazilian genius Socrates was a chain smoker; quite a few great footballers were epic boozers and pie-munchers. But, given their talent, this didn’t matter. Then sport got a bit too serious.

Late in his career, John -McEnroe was asked by a group of young players what he did to keep fit. He looked at them, baffled: ‘I play tennis.’ They had meant weight training, circuits and so forth. The question is whether, had he been born 15 years later, McEnroe would have bothered to be a tennis player at all. At some level, effort can crowd out innate ability, making sport worse, not better. Professional cycling, under this pressure, degenerated from a sport into a testbed for the pharmaceutical industry.

Not all competition is good. When determination rather than skill becomes the deciding criterion for success, you may end up favouring the dumb and energetic — arguably the worst people of all. In the 19th century, Field Marshal von Moltke reputedly categorised Prussian military officers using the following matrix — in descending order:

Intelligent & Lazy: I make them my Commanders because they make the right thing happen, and find the easiest way to accomplish the mission.

Intelligent & Energetic: I make them my General Staff Officers because they make intelligent plans that make the right things happen.

Stupid & Lazy: There are menial tasks that require an officer to perform; they follow orders without causing much harm.

Stupid & Energetic: These are dangerous and must be eliminated. They cause things to happen, but the wrong things, and so create trouble.

The working week is largely a hangover from the assembly-line age: most experiments (for instance in Utah) imply that a four-day week, sometimes with slightly longer days, can be much better. Yet there is a kind of deep-set puritan instinct which prevents us considering that shorter hours might mean more productivity; the same instinct which causes Americans to regard Germans as lazy for taking more than their meagre two weeks’ holiday — even though the Germans achieve as much in their 1,400 hours each year as Americans do in 1,800. With hindsight, ‘No Taxation Without Vacation’ might have made a better rallying cry.