Over 820,000 households could see their energy bills increase when a major service closes down next year.
These households have electricity meters that rely on the Radio Teleswitch Service (RTS) to set the rate of energy - this will charge them cheaper rates depending on the time of day.
The devices, such as Economy 7 and other multi-rate energy tariffs, pick up the different energy rates through the RTS signal - this is broadcast alongside the long-wave channel for BBC Radio 4.
Some RTS electricity meters can also automatically turn heating and hot water systems on and off during certain hours.
However, the RTS signal is set to be switched off on March 31, 2024 and these meters will no longer function in the same way.
From April next year, these meters could be left jammed on peak time electricity rates depending on when the RTS signal dies.
This could lead to huge bill spikes for households.
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Not only does it affect energy bills, but it could also alter heating systems controlled by in left permanently on or off.
New data from Elexon, the company responsible for managing the electricity balancing and settlement system, shows which energy firms have the most customers with the RTS device.
Scottish Power has the most customers with RTS meters with over 170,000 customers, next is E.ON Next with 157,000 and in third its Ocotpus Energy with 100,000.
The only way to avoid facing the issues expected to arise from the RTS switch-off is for affected households to switch to a smart meter.
Those that switch will still be able to access the multi-rate tariffs including Economy 7.
On the issue, an Ofgem spokesperson said: "Suppliers have to make sure meters are safe and accurate, and this sometimes means replacing the meter.
"We expect suppliers to communicate clearly to their customers about this."
If customers do not hear from their supplier then Energy UK recommends that they get in touch to have one fitted.
The service was originally meant to be shut off back in 2014, but energy suppliers have been keeping the service going move customers over to new meters.
In an open letter to suppliers in April, Ofgem said it was "disappointed" about the "lack of progress" on switching RTS customers over to smart meters.
The Sun reports that consultations are in place to extend the service until 2025.
Number of customers on RTS meters
- Scottish Power - 172,405
- E.ON Next - 157,069
- Octopus Energy - 100,992
- EDF Energy - 78,942
- Bulb - 63,330
- British Gas - 61,254
- SSE - 59,409
- Ovo Energy - 55,258
- Utility Warehouse - 24,538
- Shell Energy - 24,400
- So Energy - 8,866
- Outfox the Market - 5,178
- Ecotricity - 3,817
- Utilita - 3,303
- Good Energy - 2,224
