Energy bills for a typical household could hit £4,266 next year, consultancy Cornwall Insight has warned.

The higher estimate means the average household would be paying £355 a month, instead of £164 a month currently.

Cornwall cited regulator Ofgem’s decision to change the price cap every three months instead of six and higher wholesale prices for its high forecast.

But Ofgem said no forecast for next year could be “robust” at this stage and had “limited value”.

The latest price cap – the maximum amount suppliers can charge customers for average energy usage in England, Scotland and Wales for October – is due to be announced at the end of this month.

Cornwall expects this to rise to £3,582 a year, compared to the regulator’s prediction of £2,800 a year.

Dr Craig Lowrey, principal consultant at Cornwall, said its price cap forecasts had been steadily rising but the big jump was “a fresh shock”.

The energy bill warning comes as the government rejected calls for further help on energy bills until a new prime minister was in place.