Two more energy firms have said they will increase gas and electricity prices, blaming higher wholesale costs. Scottish Power said it would raise gas prices by an average of 34% and electricity prices by 9%, effective from Monday 1 September. Soon after, Npower said domestic customers would see an average rise of 14% for electricity and 26% for gas, effective immediately.

Scottish Power said it was “forced to follow other energy providers”. “These are difficult times and we understand the financial impact this announcement will have on our customers,” said Willie MacDiarmid, Scottish Power’s director of energy retail. He added that the volatility in the gas market was contributing to higher UK domestic prices. Dual fuel customers will see their bills increase by an average of 25%. Scottish Power also said it planned to spend £40m on steps to help protect vulnerable customers over the next three years. The firm, owned by Spain’s Iberdrola, is to invest £2.8bn from 2008 to 2010.

Npower said: “Today’s price rises are due to massive increases in wholesale costs which make current pricing levels unsustainable, following a price decrease in 2007 and an increase at the start of 2008.” “Until today Npower’s domestic gas prices were still the same level they were 18 months ago - whereas, during this time, the cost of wholesale gas has doubled,” said the firm. Many pensioners, already worrying about whether they can afford to heat their homes this winter, will be outraged by news of yet more colossal price hikes.