More than 9million "missing" voters could lose their voice in next month's mini general election.
They have just one day left to register or they will miss out on May 6 - when 145 local council elections, 13 mayoral polls and one by-election will be decided.
The deadline for registration is at midnight tomorrow, but almost one in five, or 17%, of the electorate have not yet registered correctly or are living at the wrong address.
Most are young renters, recent house movers or people from ethnic communities. But if they turn up at polling stations without registering they will not be allowed to vote.
Craig Westwood, the Electoral Commission's director of policy, urged voters to register online.
He said: "It only takes five minutes - the time it takes to boil a kettle."
The elections, including polls postponed from 2020 because of the pandemic, will be the first electoral test for Labour leader Sir Keir Starmer.
In the Hartlepool by-election his party is fighting to keep the seat it has held since 1974.
When is the deadline to register to vote?
Those who haven’t registered to vote have until Monday, April 19 at 11.59pm.
You only have to register to vote once, so if you’ve done it for a previous election you won’t need to take any further action.
But you do need to register your details again if you have changed your name, address or nationality since you last voted.
How to register to vote
In England, you can register to vote online or using a paper form through the government website here.
If you are completing a paper form you need to print it and send it to your local Electoral Registration Office.
You can also apply for a postal vote, but this application needs to be received before 5pm on April 20.
To be eligible to register you need to be a British, Irish or European Union citizen.
Or you can be a Commonwealth citizen who has leave to enter or remain in the UK or who does not require such leave.
You also need to be resident, or usually live in the UK, and be aged 16 or over.
But keep in mind you won’t be able to vote until you are 18.
You’ll need your National Insurance number, name and address details.
