A typical gas and electricity customer is likely to see their bill increase by £139 to £1,277 a year in October. Although the decision to lift the price cap was taken by the energy regulator Ofgem due to higher global wholesale prices, it could become a hot political potato.

The 12 per cent rise will affect about 11 million households in England, Wales and Scotland who have never switched supplier or whose discounted deals have expired. Another 4 million with prepayment meters will see an increase of 13 per cent, or £153 a year.

This represents the biggest rise since the cap’s introduction three years ago, showing that it is not much of a cap at all. It is the second increase this year: in April, a typical bill went up by £96 a year.