The two firms' bill hikes are both in effect from today.
Two more large energy firms have announced that they are putting up their general energy tariffs.
Scottish Power has said that it will raise gas prices by an average of 34 percent and electricity prices by nine percent, while Npower is to impose 14 percent and 26 percent rises for electricity and gas respectively. Both sets of price hikes have already come in to effect.
The increases mirror earlier changes by other providers, including British Gas, which imposed a 35 percent rise on its general gas tariffs.
Explaining their move, 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."
Willie MacDiarmid at Scottish Power added: "These are difficult times and we understand the financial impact this announcement will have on our customers."
The latest price rises have been criticised by charities. Gordon Lishman, director general of Age Concern, said: "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."
Adam Scorer at Energywatch, an industry group that has been fiercely critical of energy pricing in the past, added that ministers would now be under pressure to make gas and electricity more affordable. "There is strong expectation that the government will shortly announce a raft of measures to protect the most vulnerable," he told the BBC.
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