Households that have never switched energy suppliers before on average stand to slash more than £380 from their annual bills, according to research.

Price comparison website Moneysupermarket.com said more than half of the UK's 28 million electricity and gas households have never switched suppliers before, but if they did average savings would amount to more than a third (34%) a year per household, or £4.2 billion collectively.

The firm said that between 50% to 60% of households have never switched energy suppliers and use the Big Six companies - SSE, Npower, E.ON, British Gas, EDF Energy and Scottish Power.

Earlier this month, the Competition and Markets Authority in its long-awaited report into the energy market said too many households - 70% of Big Six customers - were still on more expensive standard variable tariffs and were overpaying by £1.7 billion on average a year.

Energy saving campaigners point out there are now around 30 suppliers in the UK market.

Moneysupermarket.com energy expert Stephen Murray said between 12% to 15% of households switch each year.

Mr Murray said: "A large number of them switch repeatedly because most opt for a year long deal, and when this is up, they look for the best deal in the market 12 months later."

Some customers change suppliers occasionally, while the bulk of households have never changed their energy supplier.

Moneysupermarket.com also found that London offered the biggest savings to new households that switched suppliers, with savings of 35.3%, while bill payers in Liverpool and North Wales pay the highest fees, able to make savings of 34.1%.

Mr Murray said the "relatively small" difference in these savings is down to historical networking and transmission costs that date back to when the energy markets were split up into 14 different nationalised companies.

He added: "Customers can do little about the relatively small differences between regions. The real incentive is that they can cut their annual bills by more than a third by finding the best supplier for them, within their region."