As winter approaches and temperatures drop below freezing, Pembrokeshire Citizens Advice Bureau is warning people to avoid door-to-door sellers offering cut-price electricity for their pre-payment meters after reports of a scam where people end up paying twice.

The bureau is concerned that some pre-payment meter customers are accepting doorstep offers of cut-price electricity credit, only to have to pay the full price when the fraud is detected later on. The added fear is that this bogus offer, which is already catching out many households, may become more appealing as people's energy costs rise through heating their homes this winter.

The door-to-door sellers typically offer around £50 credit for £25, using their own key to add false credit to the pre-payment meter. This process wipes all the information from the customer's original key, including any existing credit. Once the energy company is aware of the fraud, the customer is required to pay again, this time for the full amount for the energy they have used.

This scam first came to light over the summer and since then energy companies have begun warning their customers. Some customers believe they are being offered a genuine special offer, while others know that the credit is not legitimate, but find the offer too tempting to resist.

Pembrokeshire CAB county manager, Nicola Roguski, said: "These offers must seem very attractive to people already struggling with household budgets and rising fuel bills, but as with all 'too good to be true' offers, this one will cost you more in the long run.

"With winter approaching and people's energy use set to go up as they heat their homes, we're worried that what is already a problem might get worse.

"We would urge people not to be tempted and forced to pay twice, but to use a legitimate and trusted supplier like the Post Office or one offering PayPoint or PayZone, not a door-to-door seller. If you have bought credit from someone who you now think may have been bogus then we would recommend reporting it to the energy company as soon as possible as they have said they will be sympathetic to those duped. Alternatively, you can call the Citizens Advice Bureau Adviceline on 0844 477 2020 or Consumer Direct on 0845 404 0506."