Jeremy Laurance: Taking a power nap will recharge the batteries

Ken Clarke was only doing what nature intended – taking a power nap. Research shows that as little as 10 minutes of shut-eye during the day re-energises the brain, boosts memory and reduces sleepiness. It is more effective than an extra hour or two in bed.

Clarke's nap was, admittedly, earlier than expected – most people nod off after lunch, not before. The afternoon dip, as it is known, occurs even in those who have enjoyed a full eight hours sleep, eaten only a salad for lunch and eschewed alcohol in favour of water.

It is part of our circadian rhythm, generated and maintained by the body's biological clock which affects sleep and wakefulness, and mental performance. You can see its impact in road accidents caused by drivers falling asleep at the wheel. They peak, as expected, between two and six in the morning, but there is another peak between two and four in the afternoon. The early morning victims are usually young men, the early afternoon culprits older men.

Taking a nap helps to recharge the batteries. But it should not last more than 45 minutes, to avoid the deep sleep from which it is harder to recover. It may sound counter intuitive, but drinking a cup of coffee before you nap can help. The caffeine in the coffee takes 15 to 30 minutes to work, so you wake with a spring in your step.

Ken Clarke may have chosen an awkward moment to "rest his eyes" – but he has set an example to us all.