British Gas is cutting its prices for the second time in six weeks, the Centrica-owned company has said.  Its electricity prices will fall by 6% and gas by 3%, with immediate effect.  The move means its dual fuel customers, those that buy both types of energy from the firm, will save an average £40 a year from their bills. British Gas is lowering its prices in response to the falling wholesale cost of energy. It announced its first tariff cut this year in February. Since then four other companies have followed suit.  More than four million people switched their electricity or gas supplier last year in a bid to cut their bills, according to recent figures from energy regulator Ofgem. Since then, switching between companies has reached a new peak, with more than 600,000 households doing so in January and February this year. British Gas has lost about one million customers during the past 12 months. News of the price cuts come days after energy regulator Ofgem warned customers of two utility firms, EDF Energy and Scottish Power to switch suppliers. The watchdog said customers of the firms could save £140 a year, as the two companies had failed to cut their gas and electricity prices recently in line with their rivals. Between 2002 and this year, British Gas raised its electricity bills six times, and gas prices seven times, as it passed on the then rising wholesale prices to customers.