An electricity watchdog says customers are getting a raw deal from Sussex's major power company.

Ofgem, which regulates energy companies, says customers can save up to £140 by leaving EDF Energy and switching to the cheapest supplier.

Ofgem chief executive Alistair Buchanan said: "Britain's energy market remains highly competitive. Our research also shows that a big price gap has opened up leaving EDF Energy and Scottish Power customers paying over £100 for remaining loyal.

"Competition is all about customer power - in a market where over 600,000 customers switched in the first two months of this year, any supplier that tries to buck the market by not lowering their prices or failing on service risks an exodus of customers."

Ofgem estimates nearly four million people changed their electricity supplier in 2006.

EDF Energy spokeswoman Niamh Arnett said: "EDF Energy's prices are continually under review.

"We are continuing to provide competitive prices, deliver excellent service and reward loyalty to all our customers.

"We listen very carefully to what our customers are telling us and we will always do the right thing for our customers.

"Price is important but so are excellent service, social and environmental responsibility."

She said the company has one of the lowest levels of complaints of all power suppliers, and has protected consumers from rising prices through sensible management.

She claimed people who have bought their gas and electricity from EDF Energy since 2004 would have paid £240 less than British Gas customers.