Households have been urged to submit electricity meter readings to power providers before the energy cap rise on Saturday.
Submitting up-to-date readings before then will prevent companies from estimating electricity use and charging the higher rate for energy used before the price is increased, energy experts have said.
Ofgem, the energy regulator, said it would raise the energy cap to £3,549 from 1 October, but the government intervened with the energy price guarantee, which capped a typical household’s bill at £2,500.
Energy UK urged consumers to act as soon as possible to avoid energy websites crashing should millions try to upload readings at once, as was the case before the energy cap was last increased on 1 April.
The industry body said high call volumes and website traffic were expected, and recommended customers check beforehand for the best way to submit readings. Suppliers had offered numerous channels including text, email, apps and online account submissions to allow readings to be received.
As wholesale energy prices have risen, prompted in part by the war in Ukraine, so too have prices for households. Last summer the cap was £1,138 but on 1 April this year it went up to £1,971, a 54% increase.
Households will also receive a non-repayable £400 payment from the government as part of the cost of living support package, paid directly to energy accounts over six months in instalments of £66 and £67.
Frazer Scott, chief executive of Energy Action Scotland, a charity, said: “This week, every household across the UK must make sure it submits a meter reading to their energy firm to avoid paying a penny more than they absolutely have to when prices go up on October 1.
“Fuel poverty is at record levels, levels of energy efficiency improvements are simply too low to provide respite and financial support is just a sticking plaster on the deepest of wounds.”
“As unit costs for electricity and gas push bills higher still in October, communities will suffer and take years to recover. Meanwhile the impact of fuel poverty will be felt on the NHS and social care system and lives will be needlessly lost.”