By Sam Dale
Hundreds of voters have been turned away from polling stations after queuing for hours, according to reports.
Polls closed at 22:00 BST but there appears to have been a mixed reaction to latecomers.
Reports say voters were not allowed to cast their ballot in Manchester Withington, Chester, Penistone, Hackney South and Nick Clegg's constituency Sheffield Hallam.
In Birmingham an acting returning officer reportedly kept polls open to accommodate the public.
In Liverpool Wavertree voters have been turned away because the polling station ran out of ballot papers.
Liberal Democrat candidate Colin Eldridge said: "This has happened at four polling stations and it has happened in the places where I think people are most likely to vote for me."
He added that there is a "cast iron case to take this to the high court".
The Electoral Commission has issued a statement ordering a review of the situation.
"It is a cause for serious concern that many people who wanted to vote today were unable to do so by 10pm when polls closed," said the statement.
"There should have been sufficient resources allocated to ensure that everyone who wished to vote was able to do so.
"The Electoral Commission will be undertaking a thorough review of what has happened in those constituencies where people have been unable to vote."
Speaking on BBC Radio 4 Harriet Harman claimed there could be "legal challenge" by voters.
Conservative party chairman Eric Pickles called the situation "ridiculous" and said that the polls should have been kept open.
Liberal Democrat environment spokesman Simon Hughes said he "saw it coming" after seeing for himself "queues were not being dealt with as quickly as they needed to be".
Labour's election campaigner Peter Mandelson said there "may be" a legal challenge, adding that the returning officer should have allowed people in and then shut the door.