Toothless energy watchdog Ofgem was mocked yesterday over new rules to hit the big six with penalties if they do not open trade up to smaller companies.

Ofgem wants to ensure firms such as British Gas and the largest independent generators trade fairly with other suppliers in the wholesale market.

Under new rules from the end of next month, they will have to open up their finances to more scrutiny, including publishing the price at which they will trade wholesale power up to two years in advance.