The Electoral Commission will publish its interim report later into the chaos which ensued at a string of polling stations on general election day.
Hundreds of people, many of whom had queued for more than an hour before the polls closed, were unable to vote.
Problems were reported in Sheffield, Manchester, Liverpool, Birmingham, Newcastle and parts of London.
Most returning officers blamed an unexpectedly high turnout and a late surge in voting.
The Electoral Commission will examine the reasons given by officials for the problems with the 6 May poll.
Police called
BBC political correspondent Mike Sergeant says politicians on all sides were swift to condemn the chaos at many polling stations.
Some of the more alarming scenes were in Deputy Prime Minister Nick Clegg’s constituency of Sheffield Hallum, where hundreds of students queued for hours but still did not get to vote.
There were more than a dozen reports of police being called in other parts of the country, as most polling stations shut their doors at exactly 2200 BST, which the rules dictated.
But in other areas people were allowed inside – in Lewisham, south London, voting was extended for half an hour.
Among the incidents:
• Police were called to a polling station in Lewisham where about 300 people had still to vote by 2200 BST
• In Hackney, east London, angry would-be voters staged a sit-in when polls closed
• In his Sheffield Hallam constituency, Liberal Democrat leader Nick Clegg went to offer his apologies to frustrated voters at a polling station in Ranmoor, after they queued for more than three hours
• Doors were closed on 200 potential voters at Ladybarn in Withington, Manchester
• In Liverpool, voters were left waiting when one polling station ran out of ballot papers
• Voters were turned away amid long queues at St Paul’s Church in Birmingham and queues were reported at Mere Green polling station in Sutton Coldfield
• There were reports of voters being turned away after long queues in Weybridge, Surrey
• Long queues were reported at two polling stations in Newcastle
It is possible the problems might have affected the result in a few very marginal constituencies, but election re-runs are now considered very unlikely.
This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.