Gas companies have been accused of exploiting their most vulnerable customers by overcharging those on prepayment meters, according to a new report.

Consumer Focus (CF) claimed that energy companies were making more than £0.5bn a year from increased charges that they apply to customers on prepayment meters with those users typically paying £359 a year more than an equivalent user on a standard bill payment system.

Prepayment meters are typically used by customers with poor credit or income problems and have historically been more expensive than the more common bill-payment tariffs, which require the user to pay retrospectively for the energy used in a given period.

Energy suppliers have long defended the so-called “prepayment premium” by claiming that those meters require additional maintenance or installation but figures from energy watchdog Ofgem suggest that the suppliers more than make up for that outlay, with the estimated cost of a prepayment meter to the supplier being estimated at £80-£100 per year.

Energy companies are reluctant to offer bill tariffs to customers with previous credit problems, such as CCJ’s or defaults and the CF report suggests that energy companies are now making a concerted effort to move customers on to prepayment tariffs during the credit crunch.

With an increasing number of customers falling into debt with their supplier in recent months, particularly in light of inflation-busting price increases, campaign group National Energy Action claimed that more than 1,000 people per day were being encouraged to switch to prepayment meters.