Thousands of votes were not included in the result for a newly-elected Labour MP, Plymouth City Council has said.
Luke Pollard won Plymouth Sutton and Devonport with 23,808 votes. However, the actual figure including the missed votes cast in his favour was 27,283.
Mr Pollard said the votes from the Efford and Lipson ward were counted in his constituency, but they were not included in the result.
He would still have won comfortably over Conservative Oliver Colvile.
Mr Colvile’s official result on Thursday was 17,806 votes. However, with Efford and Lipson added in he won 20,476 votes.
The Electoral Commission has said it will investigate.
It is already probing claims about missing postal votes in Plymouth Sutton and Devonport, in addition to South West Devon and Plymouth Moor View.
A spokesperson said: “The commission is aware of reports of electoral administrative problems in Plymouth and is in contact with the electoral officers who are responsible for delivering the election in these areas.
“We will be reporting on the administration of the polls after the election and will carefully consider these reports as part of that process.”
The city council has been contacted for a comment.
Mr Pollard said: “It’s just another thing to add to the catalogue of mistakes by the council.
“Right from the start the city council has made a series of unforced errors.
“I want to get a sense of what has happened, why and who is responsible.
“They cannot brush this under the carpet.”