More than seven million Powergen customers are facing the prospect of big increases to their gas and electricity bills next month. The energy company, owned by E.ON, the giant German utility, was putting the final touches to a double-digit price increase for its 7.4 million British customers yesterday that could come within days. Industry sources said that E.ON’s sales teams had been called in for a briefing, fuelling expectations of an announcement soon. E.ON, with 4.7 million electricity and 2.7 million gas customers in Britain, is the country’s third-largest energy supplier, after British Gas and Scottish & Southern Energy. Three other groups, npower, British Gas and ScottishPower, have raised prices this year, blaming soaring wholesale energy prices and increased costs, caused by network upgrades and investment in low-carbon power generation. A spokesman for E.ON declined to comment. The prospect of further price rises came as rumours of a proposed merger between EDF, of France, and Iberdrola, of Spain, forced a brief suspension of Iberdrola’s shares. Such a deal would unite the fifth and sixth-ranked energy suppliers in Britain, EDF Energy and ScottishPower, which is owned by Iberdrola.