At least 4800 Scots, the majority in Glasgow, have been duped into buying false credit for their electricity meter.
Criminals across the UK have hacked the new keycard system used to top up pre-payment energy meters and are going door-to-door, dressed as power company workers, selling illegal credit at knock-down prices.
The pre-paid power meters use a key system. Normally people visit a shop to put credit on their key, which they then take home and slot into their meter.
The conmen have cracked the system and can go into people’s houses and put credit on their machine using a hacked key. If they use this, it can be detected the next time they top up their key legitimately.
Scottish Power has only noticed the scam in recent months but fear the salesman are beginning to adopt increasingly intimidating tactics. A nationwide warning will be issued tomorrow.
Gordon Irving, security director for ScottishPower, said: “These are organised criminal gangs.
“They might target places where there are elderly and vulnerable people, in blocks of flats where there would be pre-payment customers.
“They appear and say, ‘We’ve got a special deal missus, £50 of energy for £25 cash.’
“They are being really quite aggressive and threatening.
“I want to tell customers this is happening and warn them we will know about it and they will have to pay twice.”
He added: “It grows every day. For us, you could add 500 more each week. If you multiply that nationally to other main companies, it’s a massive problem.”
Tens of thousands of people have been ripped off after the scam started in London at the beginning of the year.
Conmen sell people the energy credit and then warn them that if they go back to official shops they will end up being charged for the energy they used illegally.
They then trap people and ratchet up the sales price to customers terrified they will have to pay twice -- something Scottish Power confirmed is starting to happen here in Scotland.
The fake credit is also being sold at pubs, with some customers willingly using it to help cut the cost of electricity.
Assistant Chief Constable Angela Wilson of Tayside Police is the Association Of Chief Police Officers in Scotland’s lead officer on fraud. She said: “People are using these bogus devices to effectively steal electricity.
“It must be made clear that using these illegal devices is a criminal offence.
“Users may not fully appreciate this but should ask themselves -- if something seems like to good a deal it most probably is.
“I would encourage anyone who is offered a device at less than face value to check [the person’s] ID and, if necessary, contact the company concerned.
“We will work closely with power companies to track down those involved in this unacceptable practice.”