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SSE has estimated that 16,000 households have been billed incorrectly[GETTY]

We revealed how as many as 3.9 million homes across Britain with different time slots for peak and off-peak rates could have been overcharged for years. Energy suppliers are not required to check the accuracy of meter clocks when taking readings.

The first big supplier to own up, SSE, has estimated that 16,000 households have been billed incorrectly due to two problems with Economy 10 meters. The tariff provides customers with 10 hours of off-peak electricity split into three blocks over 24 hours.

About 8,000 meter clocks are believed to have lost an hour after power cuts in winter. Another 8,000 are thought to have been installed with the off-peak times, which can vary from region to region, set incorrectly for their distribution areas.

Both faults would have caused ­families to use electricity at the peak rate while thinking they were benefiting from the off-peak tariff.

SSE has admitted that approximately 16,000 households have been paying too much because of faulty electricity meters

Gary Day, retired electrical engineer

In the wake of this, SSE announced it would check the meters of all its Economy 10 customers, with rival suppliers EDF Energy, npower and Scottish Power pledging similar probes. SSE has confirmed it will refund customers overcharged by faulty meters. Concerns about the accuracy of timed-tariff meter clocks came to light after retired electrical engineer Gary Day, from South Wales, used his specialist knowledge to spot that his clock was faulty and discovered three neighbours were also being overcharged.

Mr Day, 75, has had his meter replaced three times in the past two years by supplier Swalec, part of SSE, after finding his clock was two to three hours out or behaving “erratically”.

He secured his neighbours £2,300 in compensation and has been trying to help others concerned about the accuracy of their Economy 7 meters which provide a seven-hour block of off-peak use. He said: “SSE has admitted that approximately 16,000 households have been paying too much because of faulty electricity meters but that is only those on Economy 10 tariffs and doesn’t appear to include the tens of thousands on Economy 7.

“I have been approached in the past few days by people on Economy 7 who suspect their meters are not behaving properly, asking for help and advice.”

The Sunday Express reported last weekend how one customer resorted to a drastic measure to find out her Economy 7 hours of use.

Sue Hufton, 58, from Leicestershire, watched her electricity meter for 39 days to find out when it switched between tariffs after Scottish Power could not give her the information.

A whistleblower who used to work for British Gas has also told a national newspaper that the energy giant offered staff bonuses for selling the highest-priced tariffs to business customers, including churches and the Scouts.

Which? executive director Richard Lloyd said: “It is good to see that SSE are now taking action on this issue. It is high time the other suppliers followed suit. The industry should be taking action to fix the broken market now, they should not wait to be forced to work better for consumers.” SSE said: “Economy 7 meters are not affected by the Economy 10 time switch fault. However, it is important that we ensure the accuracy of all our meters and issues highlighted by any customer will be investigated.

“Any customer who has concerns with their meter should get in touch so we can investigate and provide the support and guidance required.”

An npower spokesman said: “We’re taking this seriously and have set up a working group to investigate fully. We will clearly act if anything is found.”

EDF Energy added: “We are currently conducting investigations.”

British Gas said: “Any customer contacting us with concerns about their meter clocks will be advised by our call centre staff on how to check the time by checking the display.

“If a customer is unable to do this we can send an engineer.”

Scottish Power was last night checking if customers were affected. E.ON could not be contacted for comment.