Customers of the ‘big six’ energy providers are spending an average of £293 more than they should be, data from independent supplier, First Utility shows.

The difference between the cheapest and most expensive tariffs is up 25% more than recorded in 2015 where the figure stood at £234.

First Utility said the overspend of £4bn is owing to the fact that more than 85% of energy customers are with the ‘big six’ – British Gas, EDF, E.on, Npower, Scottish Power and SSE – with 70% of those being on the most expensive standard variable tariff.

These customers – the majority of British households – are still not taking advantage of saving money by switching supplier.

Regionally, the biggest overall savings available are in the south and south east, while the average savings figure rises to as much as £310 in the east midlands and the east of England.

Households in south Wales have seen the biggest increase in potential savings, with an extra £80 a year now available to them, up from £221 to £301.