Energy firms Npower and Scottish Power have announced more bad news for households with steep hikes in gas and electricity prices.

Npower said prices for gas customers would increase by an average 26%, with prices for electricity customers up by 14%, both with immediate effect.

Scottish Power followed a few hours later by announcing it would increase gas prices by an average 34% and electricity prices by 9% from Monday.

The firms have 11.8 million customers between them.

Both blamed the soaring wholesale costs, saying they had made current pricing levels unsustainable.

They are the last of the country's suppliers to hit households with increases in recent weeks, following moves by British Gas, EDF, E.On and Scottish & Southern Energy.

Npower said the average gas customer would see an average annual increase of £162 with electricity bills rising by an average £60.

The firm claimed that until today its domestic gas prices had been the same as they were 18 months ago following a price decrease in 2007 and an increase in January, but wholesale costs had doubled.

Electricity generation had also been directly affected by the soaring price of raw materials prices, which had increased by 122% for gas and coal and 79% for oil over the last 12 months.

Scottish Power said the average dual fuel customer would see bills increasing by 25%. About 1.2 million of the company's customers were currently protected by fixed-price tariffs, it said. The company has offered a new tariff guaranteeing prices until December 2009.

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