Next time someone knocks on your door or telephones you and tries to persuade you to switch electricity suppliers, try to do better than a fellow who, to spare his blushes, I’ll just call ”Mr Blockhead”. According to research by two British economists, Chris Wilson and Catherine Waddams Price, Mr Blockhead managed to make himself ₤100 a year worse off by switching, rather than choose a tariff that would have saved him ₤50 a year.

Mr Blockhead isn’t alone. Another genius had such an uncompetitive tariff that he could have saved ₤150 a year - but he somehow managed to find an even worse tariff and switched to it. Of 250-odd people who had moved supplier with the avowed purpose of saving money, most picked up less than half the available gains, and about a quarter actually made themselves worse off.