has sounded the alarm for who risk huge bill hikes ahead of a major switch off. The energy giant has issued an alert to 12,000 customers ahead of the decision to switch off the Radio Teleswitch Service (RTS).

Customers with RTS meters are being urged to switch to smart electricity meters by the end of June. British Gas which is rivalled by OVO, EDF, EON and Octopus Energy has confirmed that around 12,000 meters still need to be replaced before the looming deadline. issued the warning to its customers who were still using a Radio Teleswitch Service (RTS) meter. These electricity meters rely on the RTS service to set the rate of energy.

This service charges them cheaper rates depending on the time of day and was designed to support those who use electricity for their heating and hot water.

This includes users of electric storage systems, panel heaters, or immersion heaters in water tanks, many of which typically operate on cheaper overnight rates, reports Birmingham Live.

An Ofgem spokesperson said: "We expect suppliers to consider a range of innovative solutions to ensure their RTS customers get on to a metering and tariff arrangement appropriate for them.

They added: "Smart meters are the best replacement for RTS meters - giving consumers more control of their energy usage and opening access to new money-saving tariffs - however, customers should speak to their supplier to understand the options that are available."

If you're not sure whether you have an RTS meter, there are a few things you can look out for. There may be a separate switch box near your meter with a radio teleswitch label on it and another warning sign if your property is heated using electricity or storage heaters.

If you are still using an RTS meter after the deadline you could be left with massive bill hikes.

Households with heating systems controlled by RTS could also risk having their supply switched on or off permanently. However, suppliers must ensure their service is not disrupted under Ofgem's plans.

On its website, British Gas said: "Smart meters make a good alternative to RTS meters as they have their own communication network that can do the same job as the RTS signal. We also don't install traditional meters because manufacturers aren't making them anymore.

"Smart meters come with loads of great benefits. They send your readings automatically, give you more accurate bills, and let you unlock exclusive rewards. You can even see your energy use in real time - helping you find ways to save."