Almost 14 million households are facing higher energy bills after months of increased power use during lockdown.
New research from comparison site Uswitch says we are likely to see direct debits going up by £25 a month.
Gas and electricity consumption is increasing while we are all at home during the Covid-19 restrictions.
But Government guidelines have prevented official meter readers from visiting properties to get up-to-date readings that reflect life on lockdown.
In the meantime, estimated bills don’t give a true picture – meaning many of us are facing a shock when accurate bills are calculated.
Uswitch says by the time meter-reading contractors are allowed to work again, energy debt will have built up and families are likely to be asked to boost direct debits by an extra £25 a month.
Those who read their own meters and submit readings online are likely to be asked to increase direct debits by £20. This is a slightly lower amount because they don’t have to wait for an official meter-reader and can send in readings sooner, meaning the cost is more spread out.
Uswitch says the nation will end up paying £288 million more in fuel bills.
It explained that more than two million households with traditional meters – nearly a fifth of bill payers (19 per cent) – never take their own meter readings and rely on their provider visiting their property.
With meter readers prevented from visiting homes for the last three months, it could be more than six months before these households see their bill change, meaning direct debits rising by as much as £25 a month in September.
This increase will hit vulnerable households harder, with a fifth (21 per cent) of those who rely on meter readers being over pensionable age, or having a disability or a long-term medical condition.
Meanwhile, more than 11 million households who submit their own meter readings have not done so for an average of two months and six days.
This means they last submitted readings before the UK went into lockdown and their bills do not currently reflect how much their energy use has risen as a result of spending more time at home.
The delay means these customers could face a £20 rise in their bills when their extra energy use is eventually added to their direct debits.
Uswitch is urging customers to send new readings to their suppliers as soon as possible to reduce the impact of any bill shock.
Will Owen, energy expert at Uswitch.com, said: “The lockdown has forced millions of us to use more energy, but many bills aren’t yet reflecting this.
“Two million people rely on their meters being checked for them. With up to six months since the last reading, they could see their energy costs leap £25 a month in September when their bill finally catches up with their usage.
“This bill shock will disproportionately affect the vulnerable, who make up a fifth of those who rely on meter readers.
“Checking your meter takes a matter of minutes once you know where it’s located and which numbers to report on.
“If you can give your supplier an accurate reading, they reward you with an accurate bill – rather than give you a nasty surprise later on.
“As a rule of thumb, it is worth checking your meter once a month, especially if your energy consumption has changed recently.”
Energy customers can use the Uswitch online guide to find out if their deal is ending soon and compare the best deals to switch to.