Green taxes on energy bills will more than double by the end of the decade, despite a promise by David Cameron to “roll back” the charges, according to one of Britain’s biggest suppliers. Tariffs to fund wind turbines and solar panels will drive the average gas and electricity bill towards £1,500 a year by 2020, npower says. The claim by the German-owned company raises the prospect of another inflation-busting price rise after the next election, and threatens to break the uneasy truce agreed between the Government and the energy industry. In a report published today, npower says that the cost of green levies will fall only temporarily after the Government’s decision last month to remove some environmental tariffs from bills. Npower says that subsidies to fund the rapid expansion of wind farms, solar power and biomass plants will cost households an extra £82 by 2020. Funding insulation schemes will add a further £77 to bills. In total, green taxes will add £245 to the cost of heating and lighting a home by the end of the decade, the company adds.