Set up error left 1.5m pre-payment gas customers overcharged Error in initial set-up of meters led to 'over-collection' Trade body Energy UK says customers don't have to do anything Which? says error will 'increase the low levels of trust' people already have By Ben Salisbury For This Is Money Some of the most vulnerable households have been overcharged by energy suppliers because pre-payment gas meters were not set up properly which means up to 1.5 million customers have been paying too much. Trade association Energy UK said suppliers will refund affected customers 'as quickly as possible" after a fault led to "over-collection'. It said the problem came about because up to 1.5 million meters did not work properly when they were installed, adding that suppliers 'know who is affected and have a solution'. Payment error: A mistake in the set up of pre-payment meters means up to 1.5 million customers have been overcharged Energy UK said in a statement: 'As soon as the issue came to light companies began work to fix it and arrange refunds. 'In some cases a customer's meter will have already been fixed as programmes get under way across the country. All the companies involved will be working over the coming months to get round everyone who is affected. Consumer group Which? said the error was another setback for consumers and will "increase the low levels of trust" customers already have towards the industry. The regulator, Ofgem said it had not ruled out taking enforcement action against energy suppliers. Ofgem senior partner for markets Rachel Fletcher said: 'We are determined that no consumer should lose out because some energy suppliers have overcharged some consumers on pre-payment meters. By the end of this week we expect industry to come forward with a swift timetable for resolving all traceable cases of over-charging customers, repay consumers within a clearly-agreed and publicly-announced timetable, reconfigure meters as quickly as possible and protect customers from over-payment in the meantime. Suppliers must act quickly to resolve the problem in a way that treats customers fairly. We have not ruled out enforcement action. Extra costs: Pre-payment customers who already pay a premium for energy have been overcharged Citizens Advice chief executive Gillian Guy said the error was particularly galling because pre-payment customers already pay a premium for their gas and electricity. She said: 'Prepayment meter customers are footing the bill for energy firms' errors. That overcharging has been going on for seven years shows the second-class service prepayment customers get. Prepayment meter customers are already paying higher charges than direct debit customers, so this is adding insult to injury. As a minimum customers now have a right to expect a refund on the mistaken extra charges and any interest on this money. Faulty meters that overcharge them are just the tip of the iceberg when it comes to problems experienced by prepayment customers. It costs prepay customers £80 more a year to heat and light their home, just because they use a prepayment meter. Pre-payment meters use a calorific value (CV) code to calculate the amount of gas to be charged for. But the fault meant the CV for some meters was not set properly, resulting in inaccurate readings. Energy UK said affected meters would be fixed in a roll-out starting today, and the first of the refunds were expected to be given out before Christmas. It said the industry recognised the distress this could cause and was working "as fast as it can" to resolve the problem, adding that the amounts were 'very small, and most top ups will not have been out by more than 25 pence.' Angela Knight, chief executive of Energy UK, said: 'Suppliers are working hard to roll out a solution for an issue which has affected some pre-payment gas meters. The meters were manufactured with a problem where they over-collected from customers. However, the companies know who is affected and will be getting in touch directly to put the meters right and refund any money owed. The suppliers and the wider industry are all very sorry this problem has occurred but are already getting in contact with customers. Customers do not need to do anything - their supplier will get in touch but, if they are concerned, they just need to contact their energy company who will be able to help. Which? executive director Richard Lloyd said: 'This is yet another shameful example of energy companies failing their customers and one that has hit some of the very people who can afford it least. Suppliers need to fix this fault as soon as possible and fully reimburse - with interest - the hundreds of thousands of people who have been overcharged. We urgently need major reforms to fix this market and increase the low levels of trust we consistently see in energy firms.