The websites of several energy suppliers have crashed, as customers rushed to send in meter readings before prices rise by more than 50% at midnight.
British Gas, EDF, E.ON, SSE and Scottish Power all appeared to be struggling with the volume of submissions from households looking to beat the deadline.
With energy bills due to rise by an average of 54% from Friday, millions of households have been urged to take gas and electricity meter readings the day before, to ensure they get the current, cheaper rates for all the energy they use right up until close of play on Thursday.
The problems began on the British Gas website as early as Wednesday, as people logging on to the “submit a meter reading” section were met with a message saying: “Service temporarily unavailable”.
The site was still inaccessible on Thursday, displaying a “proxy error” message. There were also reports that the app was down.
SSE customers trying to send in readings were greeted with a message that said: “Sorry, we’re working on this part of our website.”
Customers also reported difficulty submitting readings to EDF, E.ON and Scottish Power.
At midnight on Thursday, the energy regulator Ofgem is increasing the price cap, the maximum annual charge for gas and electricity.
An average home on a default tariff paying by direct debit will be hit with an increase of £693, or 54%, to £1,971, a rise that has prompted widespread concern about the spiralling cost-of-living crisis.
Experts have said stubbornly high gas prices, exacerbated by Russia’s invasion of Ukraine, could mean that bills rise to £3,000 at the next price cap decision in October.
Some of the poorest people in the UK will “simply starve or freeze” as a result, the consumer expert Martin Lewis has warned.