
An energy market investigation by industry regulator Ofgem is on track to remove more than £500m in unfair bill premiums, the watchdog has said.
Ofgem said that since the probe began, more than £300m had been taken off bills, including those of pre-payment meter customers.
It added that the big six energy suppliers had indicated that further price cuts should reach at least £200m.
However, Ofgem said the pace of delivery of the cuts had to be faster.
It said it could still refer the matter to the Competition Commission in the New Year if it is not ultimately satisfied with the industry's response to its proposals.
The £200m of additional price cuts will be for the more than four million households who are not connected to the gas grid, and others who have been identified as missing out on the best deals.
"We've seen progress but it's certainly not the endgame," said Ofgem chief executive Alistair Buchanan.
"We've seen encouraging signs since the end of our initial investigation, but we demand more and quicker action for those customers currently losing out.
"We are about to consult on new rules to end unfair pricing in future."