Vulnerable people have been left without power "for weeks" after being remotely forced onto prepayment plans by their energy firm.
Citizens Advice say they had seen a surge in the number of people contacting them regarding being forcibly moved to a prepayment meter. Calls to them relating to the issue have increased by 158%, compared to last year - translating to around 500 people.
The government has encouraged houses to get smart meters in their home claiming they increase energy efficiency, but they also allow energy firms to remotely switch a house onto a prepayment plan.
If an energy firm wanted to swap a customer onto a prepayment plan when they didn't have a smart meter the firm would need to get the customer's permission to send an engineer into their home.
The energy firm is meant to discuss changing their customer onto a prepayment plan with them, but the energy regulator Ofgem claims it has seen examples of them not doing this.
Ofgem said: "We’ve become aware of possible failings in how some suppliers treat vulnerable smart meter consumers, including some customers being switched to prepayment meters without full regard to the customer’s situation."
Ofgem said they had heard of vulnerable people being left without power for weeks because they had been switched to prepayment plans.
They said: "In extreme cases the reports we’ve received suggest this has led to some vulnerable customers being left without power for days or even weeks. "Completely unacceptable, especially as we head into a very challenging winter."
The installation of a prepayment meter is usually the last resort for debt collection, meaning many of the people who had been forced into this situation will already be struggling with their finances.
This means the prepayment meter will now have to be topped up to get gas and electricity to their property at a time when they were clearly already struggling with money.
Prepayment meters also tend to be more expensive than using credit because they miss out on the best fixed-rate tariffs.
Gillian Cooper, Head of Energy Policy at Citizens Advice, said: "Forcibly moving people in debt onto prepayment meters is disconnection by the backdoor. If people can’t afford to top up, they’re at real risk of the heating going off and the lights going out.
"The government must ban energy suppliers from using these tactics this winter. And Ofgem has to ensure energy companies aren’t chasing people for arrears they simply can’t pay."The UK has around four million prepayment customers, which has stayed relatively stable for the past 10 years.
They remain a preferred method of payment for many to allow them to budget more effectively.
Around 50% of homes in the UK have smart meters, two million of these are on prepayment plans for electricity and 1.5 million for gas.
Ofgem said they had written to suppliers to learn more about the issue and to remind them of their obligations to customers.
They said they won't "hesitate to take action off the back of this work where failings are found."Ofgem also said they will soon be releasing ratings of each energy firm with regards to how they support vulnerable customers, and forced switching to prepayment plans will be factored into this.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know