The rise comes despite Chancellor George Osborne calling on energy firms to reconsider the price rises that have sparked warnings of more households being plunged into a "long, cold winter".
Adam Scorer, director of energy at Consumer Focus, said the rush of price hikes from suppliers will fuel consumer concerns about the energy market.
He added: "No one welcomes a price rise. But when half the market raises prices in just four days, consumers will question whether this is in response to volatile commodity costs or simply pack behaviour."
The price increase for Scottish Power's direct debit customers will be 8.7%, compared with the 1.4% rise for quarterly cash and cheque customers. Around 700,000 households will not see an increase as they are on one of the company's fixed price or capped tariffs.
EDF has yet to make an announcement about prices, while E.ON has guaranteed a price freeze for 2012.