Ofgem is to begin publishing an energy company league table from today comparing the most expensive standard tariffs with the cheapest deals on the market to provide greater transparency to consumers.
Energy Secretary Greg Clark said the table will instantly show consumers where they can save money and increase transparency around the "millions" of Britons who are overpaying for their energy by remaining on the expensive standard variable tariffs.
The table will compare the average energy bill paid by a household on a standard variable tariff with the larger energy companies with deals from the 10 cheapest suppliers.
The Government is also launching a call for evidence on allowing customers access to accurate electronic data on how much energy they use to enable them to share it securely with price comparison websites in return for individual quotes.
The Competition and Markets Authority (CMA) warned in June that 70% of people were on the more expensive "default" standard variable tariff, costing consumers £1.4 billion more than a competitive market.
Ofgem said just last month that 66% of all households remain on standard variable tariffs.
Mr Clark said: "Millions of people across Britain continue to pay too much for their energy. The measures announced today are a positive step to help more people benefit from increased choice and competition.
"As the Government has made clear, where markets are not working for consumers - in energy or otherwise - we are prepared to act."
Citizens Advice chief executive Gillian Guy said: "This league table will lift the lid on the price difference between standard tariffs and cheaper deals, helping those customers who are currently paying over the odds for their gas and electricity identify a better rate.
"We'd also like to see energy companies do more off their own back to help customers who are on a low income, like moving them to a cheaper deal."
Meanwhile, Energy UK figures released today show that more than four million customers switched electricity supplier this year, "eclipsing" the past three years, while more than 400,000 switched in November - the highest figure since November 2013.
Energy UK chief executive Lawrence Slade said: "A record number of people have switched electricity supplier in 2016. This is fantastic progress, but more needs to be done.
"Over 40 companies across the industry, big and small, are working hard to win customers. I'd encourage everyone to look at the best deal for them, whether that is one that offers a lower price or better customer service, there are choices for everyone."
The Ofgem league table can be viewed on its website from 10am on Wednesday.
Richard Neudegg, head of regulation at uSwitch.com, said: "This could be the wake-up call consumers need. Two thirds are needlessly overpaying for their energy by almost £200 a year. Anything that helps people take advantage of competition in the market is to be welcomed.
"While a league table of prices based on average energy use will be helpful, households should always run a personalised comparison, based on their own usage and location, to find the best deal for them. Making it easier for consumers to access their own consumption data will help them cut through complex bills and find a better deal more effectively."