Plymouth City Council has commissioned an independent inquiry after 1,500 postal vote forms were not sent out prior to the general election.
The council issued a statement on the day before the election to say the problem was caused by an IT issue and voters had been issued with emergency replacements.
However, the council said emergency proxy votes for people living abroad were not permitted under the circumstances. LGC has asked Plymouth to confirm the number of people affected.
Plymouth chief executive and acting returning officer Tracey Lee confirmed an investigation would take place soon after the problems came to light.
It also emerged on the day after the election that 6,000 votes were missed off the final declaration in the marginal constituency of Plymouth Sutton and Davenport. Luke Pollard (Lab) took the seat from the Conservatives. When the 6,000 votes were included, it showed a larger majority for Mr Pollard.
It has also been reported locally that the constituencies of Plymouth, Moor View and Plymouth, South West Devon were also affected. LGC has asked the council for confirmation.
The investigation will be led by Dave Smith, former chief executive of Sunderland City Council, who sits on the government’s elections and referendum steering group.
He also leads on elections and democracy for the Society of Local Authority Chief Executives & Senior Managers.
Leader Ian Bowyer (Con) said he was “deeply concerned” by the problems with the election and people affected by the election administration problems have been asked to submit evidence to the inquiry.
Cllr Bowyer said: “I have asked that the investigation makes every effort to hear evidence from as many people in Plymouth as possible who have been affected by the problems. This way the investigators will be able to better understand the problems, how and why they happened and how many people were affected.”
The scope of the inquiry will include processes and controls around election planning, an assessment of the overall numbers of voters affected and the “capacity and capability” of the elections team.
Questions were also raised when many people reported being turned away from polling stations in Plymouth. The council said this was due to election registration forms not being completed properly.