Peter Rhodes on the menace of maths, shopping limits and students – the new Typhoid Marys

This made me smile. It's an internet warning that in order to stop panic-buying, supermarkets are imposing maximum purchase levels, as follows. Asda: two hand sanitisers and a four-pack of toilet rolls. Tesco: one hand sanitiser, 500g of rice and a four-pack of toilet rolls. Waitrose: one lobster, six quails' eggs and 100g of foie gras. Aldi: one welding kit, a pink sports bra, two trumpets and a wetsuit.

If the above seems familiar, it has been around some time. The earliest reference I can find is in the Jakarta Post of March 19.

According to an ancient Persian legend I just made up, a mighty king once challenged a wise old philosopher to a game of chess, offering him any prize he wished if he won. The old man meekly asked for nothing more than a single grain of rice to be laid on one square of the chessboard, two grains on the next square, four on the next and so on. Each move on the 64 squares doubles the amount.

The mighty king cheerfully agreed but discovered as the game progressed that the total amount of rice he would owe the old man was 210 billion tons, or enough to cover the sub-continent of India in rice to a depth of one metre.

In the traditional version of this tale, the philosopher becomes the richest man in the world, and the moral is that knowledge is more powerful than the mightiest king. In my version, the mighty king orders his guards to chop off both the old man's hands and says: “Okay, grandad, your move,” and the moral of this version is that nobody likes a smartarse.

Another moral is that pure maths needs taking with a pinch of salt. Take last week's Armageddon forecast by the Government's chief scientific adviser Sir Patrick Vallance. He warned that if the number of Covid-19 cases continued to double every seven days, by mid-October we would have 50,000 new cases per day. But why stop there? If you keep doubling every seven days, the maths tells you that the entire UK population will test positive in the week before Christmas which is about as likely as the old man getting his rice.

No-one should blame the authorities for warning us of the very real dangers of infection. But if they overplay the maths and their direst scenarios fail to happen, Joe Public may think he is being conned. And when the people stop believing the experts, the virus thrives.

Sage, the Government's Scientific Advisory Group for Emergencies, says university students may become the Typhoid Marys of today's pandemic. It warns: “A critical risk is a large number of infected students seeding outbreaks across the UK.” Will we perish by degrees?