An IT error has resulted in some people who are not registered to vote being "wrongly informed" they can take part in Thursday's general election.
The Electoral Commission said a glitch in software used by some councils had led to a "small number" of ineligible people being told they could vote.
The watchdog said it was working with those councils to ensure those affected did not turn up to vote in error.
Registration for the election closed on 26 November.
Anyone aged 18 or over can take part in Thursday's election, as long as they are a British citizen or qualifying citizen of the Commonwealth or Republic of Ireland. However, they must have registered to vote by last month's deadline.
It is understood the error related to software supplied to councils by Electoral Reform Services, which helps run elections on behalf of local authorities and other organisations. It is not clear exactly where the error occurred.
The firm was bought by the IT services firm Civica Group last year.
The Electoral Commission said it only became aware of the issue on Wednesday morning, less than 24 hours before polls open.
"We are aware that some local authorities have been impacted by a software issue that has resulted in a small number of people being wrongly informed that they can vote on 12 December," it said in a statement.
"The Commission has issued guidance for authorities to help ensure that those individuals affected are contacted and given the correct information. Only those eligible and correctly registered will be able to cast their vote on polling day."
Polling stations open at 07:00 GMT on Thursday, with voting continuing until 22:00 GMT.