Consumers appear to be developing a heightened awareness of the environmental impact of their energy use - it is, after all, hip to be green - yet in outlining the problems and prospects for Britain's energy future in his podcast for The Times, Allan Asher, the chief executive of energywatch, highlighted another less fashionable concern - fuel poverty. In particular, he singled out the contentious pre-payment meter (PPM) system.

Customers with PPMs must buy tokens or charge a key or card to keep their meter in credit and the energy supply turned on.

According to energywatch, such customers can end up paying their supplier as much as £194 more per year than those who use the same amount of power but are able to pay by direct debit.

In October 2007, energywatch said that there were 3.5million electricity PPMs and 2.3million for gas in use across Britain.

Customers with PPMs tend to be living on low incomes. Indeed, about a third of those claiming state benefits, single parents, the unemployed and those who suffer from a disability or long-term illness have one. They are also used as a means of debt recovery: energywatch said that since 2002 approximately 1.4million PPMs had been installed because of consumer debt.

“Those sorts of differences [in bills] shouldn't be allowed and forcing the poor to pay more for power and gas is just immoral in today's society,” Mr Asher said.

However, Julian Mears, a spokesman for British Gas, said: “There's a slight misconception [about PPMs]. ]A lot of people think it's only the fuel poor who use PPMs, but a large percentage of people like them for budgeting.”

Mr Mears said that a PPM was more expensive than normal meters because of the service costs involved in maintaining the metering equipment and the PayPoint services that enable customers to top up in local shops.

Last year Ofgem calculated that service costs for dual-fuel pre-payment customers was £85 a year: energywatch believes that the cost is much lower and has urged the regulator to further investigate the issue.

Steps are also being taken that could help those on low incomes. Energywatch, the Energy Retail Association and the leading power suppliers are backing proposals to roll out Smart Meters across the UK. These meters, which would mean an end to estimated bills, send more accurate information about energy consumption directly to the supplier, in real time. By enabling a more efficient use of power, they can both cut bills and lessen the environmental impact of energy use.

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