Scottish Power said 2.4 million households in the UK would see their bills increase Scottish Power is to raise the cost of gas by 19% and the cost of electricity by 10%.
The utility firm said the increase, which would affect 2.4 million households in the UK, would come into effect from 1 August.
Affected customers will see an average daily rise to a dual fuel energy bill of 48p per day.
The company said the move reflected sustained increases in the wholesale energy market.
However, it said about 700,000 households would be protected by capped or fixed priced deals.
Scottish Power, which is part of Spanish company Iberdrola, last put its prices up in November, when gas prices rose 2% and electricity bills went up by 8.9%.
Other suppliers are widely expected to follow Scottish Power’s lead over the coming weeks.
Raymond Jack, Scottish Power’s UK retail director, said: “Wholesale prices for gas and electricity have increased significantly since the end of last year and continuing unrest in global energy markets means future prices are volatile.
“We understand times are difficult for many people, and we have done what we can to absorb these additional costs for as long as possible to minimise the impact on our customers.”
The power company has also launched an new online product with a long fixed-price offer that it claims is one of the cheapest in the market.
Scottish Power said it could also help its customers to reduce their fuel bills by making energy efficiency savings in their homes.
Mr Jack added: “Some of our customers could save an average of £459 per year by making simple changes to the way they pay for their energy, switching to paper-free online billing and selecting one of our new or existing energy products.”
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