September 7, 2010 - In the most dramatic scam to hit the industry, over £2 million has been illegally obtained by doorstep sellers from 85,000 customers, who thought they were signing up to a special deal. The scam has hit prepayment customers who pay for their electricity in advance through a key, or card, they put into their meters.

Energy UK, the trade body that represents the major suppliers, along with Consumer Focus, the watchdog, have warned all the 3.5 million households with a prepayment meter to be vigilant.

Criminal gangs are employ door-to-door salesman offering householders £50 worth of credit on their electricity meters for £25. Once the customer has accepted the offer, the salesman uses a card or key to top up their meter, which appears to be correctly credited.

However, the energy company can tell the credit has been obtained from an illegal source, and the vast majority of customers have found later on, when they next go to top up their card, they need to pay – the full £50 – for the electricity again. Only a "handful" of the most vulnerable customers have been let off having to repay the full amount.

It is understood the scam has been running since at least June, with all customers of all the major energy companies affected.

The UK Police have been working with the energy companies but no arrests have been made.