Fraudsters call retailers and take gas meter readings, which are then used to make up contracts with new suppliers without the store owner’s permission.

A senior British Gas source told betterRetailing: “It does happen, and suppliers don’t really care as long as they are getting new customers and they aren’t making too much fuss.

“The industry’s code of conduct says disputes have to first be dealt with between the customer and the broker, rather than the supplier itself, even if it was fraudulently done.”

Bolton retailer Vas Vekaria warned: “The first thing you’ll know about it is when you get a bill.”