About 100 people were turned away from a Lancashire polling station after long queues prevented them from casting their votes before the polls closed.
People who arrived at Longsands Community Primary School to vote in the Ribble Valley constituency were faced with long queues from about 2030 BST.
When voting closed at 2200 BST, 80 to 100 people in the polling station were told it was too late to vote.
Lancashire Police have said they will be investigating the incident.
Returning officer David Morris told the BBC he had contacted Preston City Council to ask for more staff to be sent to help reduce the queues.
When they were unable to provide more staff at the scene, he contacted Lancashire Police who advised him that polls should close at 2200 BST and the ballot boxes should be collected as they were.
Mr Morris added that the council would be looking into the incident further on Friday.