Millions of households across the UK are missing out on a total of £2.7 billion of potential savings by not switching energy suppliers, experts have warned.
Those who shop around could save an estimated £250 a year each, as analysts warn most British bill-payers are being overcharged - and say recent "paltry" price cuts from the Big Six energy firms have given customers "false confidence" that they are getting a good deal.
An analysis of energy bills collected by Department of Energy and Climate Change's Domestic Fuel Inquiry compared the data with the cheapest available deals.
And it found that around 13.5 million households in the UK could benefit from moving.
The figures have been released as part of the government's new Power to Switch campaign, launched today, which encourages people to get the best deal for themselves.
It comes amid mounting criticism of the Big Six energy firms - British Gas, npower, E.ON, EDF, SSE, and Scottish Power - who announced cuts in average gas tariffs of between 1.3 per cent and 5.1 per cent, despite wholesale gas prices reportedly plummeting by around 20 per cent since December.
MoneySavingExpert's Martin Lewis urged people to take the time to shop around.
We need to shout loud about the benefits of switching tariff. Too many people think energy firms are 'all the same'. That's far from true, there are huge differences on both price and customer service.
The campaign has also won the support of the country's largest independent energy provider, First Utility.
The Big Six's recent price cuts gave savings of less than £30 to those customers on their standard variable tariffs, yet switching to the cheapest deals on the market could save you £260 on average.