CUSTOMERS of the Big Six energy firms have paid an additional £7.3 billion in charges in the past five years, says a report.

Ofgem data compiled by energy provider Bulb found households who held accounts with the biggest players – including British Gas, SSE, E.ON, Npower, EDF and Scottish Power – for at least five years paid out an average £853 more than they needed to over the period.

Cheaper fixed tariffs offered to new customers commonly expire within one or two years, at which point customers are usually transferred to standard variable plans which cost up to 30 per cent more than their original deal.

The report claims the so-called “loyalty fee”, which measures the annual price difference between the average standard variable tariff at a Big Six firm compared to their cheapest tariff, is £852.57 for the typical household over five years.

Hayden Wood, co-founder of Bulb, said: “These latest numbers show that so-called standard tariffs no longer have the customers’ best interests at heart.”

A recent poll by uSwitch found a third of households are already concerned about paying their energy bills this winter and more than half are struggling with household finances.

British Gas became the latest Big Six energy supplier to hike prices at the start of August, when it confirmed that it was ramping up the cost of electricity by 12.5 per cent for 3.1 million customers, despite falling wholesale prices.

Rivals including Scottish Power, E.ON and EDF raised their own bills near the start of the year.

Competitor SSE raised dual fuel prices by 6.9 per cent in April, while Npower came under fire in February amid plans to increase gas and electricity prices by 9.8 per cent, a move that added £109 to annual dual fuel bills.