In total, 900,000 Scottish Power customers on a standard variable tariff will pay on average £117 more a year from 1 April, taking the average bill up to £1,254. This is in line with the increase to the energy price cap announced a fortnight ago by the regulator Ofgem.

Prepayment meter customers will also face a £106 or 9% price rise.

Scottish Power is the second supplier to increase prices today, after British Gas announced it was upping bills this morning.

Five of the big six energy companies have now confirmed price rises since Ofgem said the cap would be going up from 1 April.

Richard Neudegg, head of regulation at uSwitch, said: “Standard tariffs are not value for money, with or without a cap, and Scottish Power customers have been given a harsh reminder of this today.

“But households don’t have to fork out extra just because a spreadsheet says so.

“There are nearly 200 energy tariffs which are currently cheaper than the new price cap will cost. Consumers can grab savings of over £300 by switching now.”

What is the price cap?

The energy price cap came into force on 1 January and was meant to give customers on pricey standard or default tariffs a better deal. It was originally set at £ £1,137, saving the average household £76 a year,

Suppliers were forced to cut the cost of the tariffs so that the typical dual fuel customer would not pay more than the cap.

However, the cap is reviewed twice a year to take into account the cost of wholesale prices.

Earlier this month Ofgem said the cap would go up to £1,254 from 1 April. Within days, suppliers had begun to announce price hikes to their standard tariffs.

Experts say more than £1bn is expected to be added to energy bills from April.