Energy firm npower has joined SSE and British Gas this week as the third major supplier to announce price rises, with a dual-fuel bill to go up 10.4%.

The increase, which includes an electricity price rise of 9.3% and a gas price rise of 11.1%, will take effect on 1 December, and is the highest increase announced so far.

SSE will increase prices by 8.2% from 15 November and British Gas said prices would go up by 9.2% on 23 November.

Secretary of State for Energy, Ed Davey, says he is extremely disappointed by the price hikes and has urged customers to make savings by switching to one of the smaller, cheaper suppliers.

In response to the British Gas enouncement he said: “This is extremely disappointing news for British Gas’s customers, and the company will need to justify this decision openly and transparently.

“The competition we’ve introduced to the energy market means people have a choice. They can look for the best deal available; including from smaller suppliers, with the confidence that switching will make an immediate difference to their bills and force the Big Six to compete on price.

“I recently wrote to energy companies asking them to publish their costs of delivering the Energy Company Obligation. Today’s announcement shows why that’s necessary, because British Gas’s ECO numbers just don’t add up when you look at what other energy companies are saying about their costs.”