Ofgem says the proportion of households on standard variable tariffs ('SVTs') who pay by non-prepayment methods was 59% on average between October 2016 and April 2017.
How much can you save without switching?
The regulator estimates that around 14 million households are on SVTs and have the potential to save hundreds of pounds a year on cheaper tariffs from their existing supplier.
It has compared the average Standard Variable Tariff of the UK's 10 biggest energy suppliers to each provider's cheapest available deal for non-prepayment customers.
Note that these prices are based on data from June earlier this year, but it's a good snapshot of the potential savings you could find without having to go through a switch.
This image gives you a rough idea of the savings. For the exact amounts, scroll down to the table beneath it.
Proportion of customers on SVT
Average annual SVT bill
Supplier's cheapest annual average tariff in June 2017
Potential saving by moving
Source: Ofgem All tariffs shown are for a domestic customer with typical 'medium' consumption (3,100 kWh/year for electricity and 12,500 kWh/year for gas).
Two thirds of Coop energy customers could have saved £260 a year by moving onto a better deal with the supplier in June.
Meanwhile over half of npower customers could have pocketed £249 a year by signing up to a new deal.
Are you paying over the odds?
A standard variable tariff or SVT is an energy deal that doesn't have a fixed-term and is variable which means what you pay for energy can go up or down.
All suppliers have an SVT, but it's typically more expensive than its other deals.
If you do not pick a specific plan when an introductory deal ends you are usually dumped onto the SVT until you choose a new one.
Save even more
If you think you are paying more than you should for your energy you should check to see if your provider is offering something better.
But to save the most amount of money you should compare deals across a range of providers and go for the cheapest deal you can find.
Currently, the cheapest dual fuel energy deal on the market costs £824 a year which means the potential savings are much higher when you chase the best deal.
Npower customers, for example, could save £363 instead of £249 by going for the cheapest deal available.