Energy regulator Ofgem slapped a £1m penalty on British Gas, a unit of Centrica, for misreporting the amount of electricity supplied under the government's renewables obligation. Ofgem said the error was caused by incorrect representation of the reporting requirements and insufficient procedures by British Gas, the country's biggest household energy supplier. British Gas underestimated the amount of electricity it supplied, by an average of 0.62% per year, over a period of seven years. Ofgem administers the Renewables Obligation that requires energy suppliers to provide evidence of the amount of electricity supplied from renewable sources relative to total electricity supplied.Ofgem said the financial penalty on British Gas was "significantly reduced" as the company had approached the energy regulator with its error. The energy regulator reminded other suppliers the penalty for incorrect reporting and indicated that this action is a "clear warning to all companies reporting under the renewables obligation."Earlier this year, Ofgem imposed a penalty of £8m on National Grid for misreporting on a gas mains replacement programme between the years 2005 and 2008. AR