Npower to raise energy prices by 10pc Npower chief executive Paul Massara said: "I know that any increases to household bills are always unwelcome, and this is not a decision that we have taken lightly. We will continue to take steps where we can to reduce the impact of the external influences on energy bills. Npower said approximately 3.1m customers will be affected by the price rise. Around 500,000 customers have fixed their prices and are not affected by the price increase. Labour leader Ed Miliband has said that he would freeze energy prices for 20 months if his party wins power at the 2015 election. Mr Massara said: "We understand that although the Labour Party's proposed price freeze may appear superficially attractive it will not lead to lower sustainable prices going forward because it doesn't cut the growing costs of supplying energy. Only 16pc of the bill is under our control and imposing price controls discourages investment, increases uncertainty and ultimately leads to higher prices. Npower said the increase will add £137 to bills each year. The company last increased prices in November 2012 by 8.9pc. Clare Francis, editor of MoneySuperMarket, said: "Npower is the third of the Big Six energy firms to announce a price hike, and with three million customers hit with increases, even more UK households are feeling the pressure. In total 17.1 million households will now see their energy bills rise between November and December unless they take action. Find the cheapest energy deals Last week British Gas raised its household electricity and gas by an average price of 9.2pc, just seven days after SSE announced an 8.2pc rise. E.On is tipped to follow suit with an increase of its own this week. Scottish Power and EDF energy are the other main providers and are yet to make announcements on their winter pricing. Npower's move followed fierce criticism of the sector by the Archbishop of Canterbury. The Most Rev Justin Welby said on Sunday that energy firms had to be "conscious of their social obligations" and "behave with generosity and not merely to maximise opportunity." The announcement from npower came as Britain sealed a deal with French energy EDF to build the first nuclear power station in a generation at Hinkley Point in Somerset, following months of negotiation. Richard Lloyd, exec director at consumer watchdog Which? said: "Three of the Big Six energy companies have now announced inflation busting price hikes just before the winter kicks in, piling on the squeeze for already hard-pressed consumers. We now need an independent expert review, that reports to Parliament, of all Government energy policy and wholesale market costs, with an assessment of whether consumers are getting value for money and where savings can be made. The Telegraph Energy Comparison Service - Compare energy prices and fix to a cheaper gas and electricity tariff.