Five of Britain’s “Big Six” energy suppliers have been accused of breaking rules designed to protect their poorest customers

The National Housing Federation (NHF) claims Scottish Power, British Gas, Scottish & Southern Energy, npower and E.ON breached new licence conditions, which set a cap for how much more pre-paying customers can be charged than those settling bills by direct debit.

Introduced two months ago, the ruling requires energy companies to charge no more than the extra costs incurred in paying by meter.

Ofgem – the energy industry regulator – imposed a limit of £88 on the differential in September following a major investigation into whether six million pre-pay customers were being penalised.

However, companies are still charging up to £20 more than the £88 addition. E.ON charged pre-pay customers £99 more than those on direct debits, and Scottish Power billed pre-paying customers £108 extra.

The average excess charge was the same as that billed in August, the month before the new rules came in. Many people who use pre-payment tariffs are unemployed, pensioners, disabled or on a low income.

The average wage of a pre-payment customer is £13,500 a year, almost half the national average.

“This means they [the regulator] failed to make any difference,” the NHF complained, claiming its findings cast fresh doubt over Ofgem’s ability to “tame” the £27 billion-a-year energy industry.

NHF chief executive David Orr, who described the situation as “an absolute disgrace”, has written to Ofgem demanding an investigation into whether firms have breached their licence conditions and claimed the regulator is not taken seriously by members of the industry. The NHF represents 1200 housing federations in England.

Mr Orr said: “EDF, SSE, npower, E.ON and Scottish Power are to be commended for equalising their pre-pay tariffs with those customers on quarterly bills.

“However, the fact that five of the Big Six energy companies have already ignored the new licensing conditions shows that Ofgem isn’t taken seriously.

“Ofgem has lost the confidence of millions of pre-pay customers across the country. Ministers now have a duty to end the pre-pay meter rip-off once and for all.”

A spokesman for Ofgem said: “It is a fact that price differences between pre-pay meters and other payment types have fallen sharply.

“We will continue to monitor suppliers’ compliance with the licence conditions and if differentials cannot be objectively justified we will investigate.”

He insisted that the widespread abuse of pre-payment customers had ended, because the difference in bills was much lower than in the past.

Industry body the Energy Retail Association (ERA), which represents the Big Six, denied its members were infringing their licence conditions.

A spokeswoman said the principle of a fair reflection required by the licensing agreement did not specifically state a cap of £88 as the maximum difference allowed between pre-payment meters and direct debit.

She said pre-payment meters inherently incur a higher cost due to the infrastructure they require.

“Ofgem has put in place rules that make sure all customers – not just those on pre-payment meters – are charged fairly according to what it costs suppliers to provide them with their energy,” the ERA said in a statement.

“This is not a price control as the NHF suggests. Energy suppliers have already taken action to reduce pre-payment tariffs, and in some cases, using a pre-payment meter now costs less than paying by standard credit.”

Between 2006 and 2008, power companies made £464 million in “unjustified charges” by billing above the costs of maintaining pre-payment meters.