Hundreds of people were unable to vote as they were still queuing when the ballot boxes closed at 10pm.
Voters were turned away in Hackney, Hull and Lewisham, according to reports.
A Sky News viewer said people were unable to vote in Weybridge, Surrey, at the Oatlands Park polling station.
There were reports of similar situations in other parts of the country.
Voters in Hackney, east London, said they were turned away from a polling station in Triangle Road after some had been forced to queue for more than an hour and a half.
They staged a sit-in protest at the building after the ballot boxes closed and police had to be called.
And officers were called to a polling station in Manwood Road, Lewisham, south London, where around 300 people had yet to vote by 10pm, Scotland Yard said.
The Electoral Commission said it would be undertaking a “thorough review” of what had happened in constituencies where people were unable to vote.
A Conservative party spokesman said: “These are very disturbing stories which clearly need to be thoroughly investigated.”
Asked if the situation amounted to a “scandal”, Olympics Minister Tessa Jowell replied: “I think it is.
“These are queues of people exercising their democratic right and then being denied it.”
More follows…
SKY – Protests As Voters Turned Away In Hackney, Hull And Lewisham | Politics | Sky News
video footage there
