Electricity and gas suppliers have been warned that they would be fined if they continue to send invoices to customers for money they are not allowed to collect.
The energy regulator ofgem told BBC’s Money Box which he wrote to the chiefs of chief demanding to know how many people have been returned to “invoices”.
Back billing is when customers receive new energy bills used more than 12 months ago – a practice prohibited seven years ago.
A senior boss in Ofgem, Tim Jarvis, told the BBC that he had been shocked and disappointed after hearing some of the BBCs had investigated.
Although it was prohibited in 2018, the invoicing of the back still arrives at thousands, even tens of thousands of people.
The suppliers have apologized, but say that tens of millions of invoices are sent each month.
Earlier this week, the energy secretary, Ed Miliband, wrote to the regulator exhortant to “challenge the illegal billing of billing”.
Mr. Jarvis said that he had now written to the heads of the management of the big energy suppliers by asking that they discover the real scale of the problem, adding that the regulator will not hesitate to amend any business that has systematically violated rules.
Citizens Advice received 47,000 complaints concerning invoicing in general in 2023, going to nearly 60,000 in 2024.
