Energy regulator Ofgem has stepped up its investigation into the 'big six' suppliers. Five months ago Ofgem said it had evidence the leading energy companies had pushed up prices in response to rising costs more quickly than they reduced them when costs fell. An Ofgem statement said: "Ofgem has appointed accountancy firm BDO to provide recommendations on how best to improve accounting disclosures by energy suppliers" in a bid "to improve accounting transparency."