Labour squared up to toothless energy watchdog Ofgem yesterday after it said it was not capable of investigating the party's claims that energy companies are ripping off the nation by inflating every household bill by £50 a year.

The so-called big six - British Gas, SSE, Eon, EDF, npower and Scottish Power - paid £4 billion more for power than the market rate by buying energy produced in their own power stations, according to shadow energy secretary Caroline Flint.

Labour said this had cost each household £150 over the last three years.