ENERGY companies should account to their customers for the latest round of price rises, amid new evidence that they are outstripping increases in the wholesale costs of gas and electricity, Downing Street has said.

Figures from industry regulator, Ofgem, show that while price rises announced this autumn by companies averaged 9.1%, wholesale prices rose just 1.7% - adding just £10 to the average household bill of £600.

The Prime Minister's official spokesman said: "It is for the energy companies to explain the decisions they have taken around bills to their customers."

Labour said the figures showed that the Government was failing to get tough with the companies amid mounting public concern over the soaring costs to households.

Also this week, Energy Secretary Ed Davey will set out details of the annual competition test for the energy market - announced last week by the Prime Minister - to be carried out by Ofgem in conjunction with the Office of Fair Trading (OFT) and the Companies and Markets Authority (CMA).

Mr Cameron, speaking at the Mini plant in Oxford, stressed the importance of opening up the market to new entrants.

"I'm frustrated about the Big Six. I want to see the Big 60, I want to see many more energy companies," he said.

Angela Knight, chief executive of Energy UK, said: "The energy suppliers which have announced price increases highlighted a number of areas where costs have risen. In particular, they have pointed to the 'pass throughs' on to the bills, such as levies.

"Although wholesale costs have risen, this is not the only reason for the recently announced increases.

"Companies do not buy wholesale energy just at this week's, or this month's, prices. They contract for long periods ahead to give security to their customers.

"As a result, what a company pays for wholesale energy in any one year will be a mix of rates. Therefore, they are reporting the actual cost as opposed to the theoretical calculation set out by Ofgem."