Election watchdogs have demanded new safeguards to prevent postal voting fraud which they say has undermined confidence in the electoral system.
Postal votes were requested by around five million voters
Electoral Commission chairman Sam Younger called for voter registration to be improved by people being asked to produce a signature and an address.
The Lib Dems are considering a legal challenge to results in Birmingham Ladywood where they lost to Labour.
Radio 4 presenter Mariella Frostrup said she was a victim of vote fraud.
She arrived at her polling station with her young child, and found: "There was a line through my name so I couldn't be allocated a ballot paper."
She said she was "apoplectic".
Up to four million people are believed to have requested a postal ballot at this general election.
Mr Younger said even though the number of challenges that were predicted had not materialised, the public's confidence in the system had been "knocked".
"It is urgent, it seems to me now, that the government - and I hope with the co-operation of all parties - will actually see as a high priority looking to implement a number of changes, many of which we have had in the public domain and recommended for the past two years to underpin the security and the administration of the system."
The government has come under fire for not implementing the commission's recommendations of tougher measures to protect the postal voting system.
Mr Younger said he was "disappointed" the government had not acted over his suggestions, but said he would be surprised if there was not a "consensus" now around his recommendations.
He said the registration system needed to be reformed to its "core", with better definition of electoral fraud offences to which make it easier to prosecute.
At the core of this would be "proper identifiers of individuals on the register" including the requirement for a signature and a date of birth to be provided, he said.
Currently voters cannot be required to provide identification when they turn up to vote.
The Daily Telegraph features a letter from a voter, John Lally, who witnessed a girl who "could not have been more than 12" turn up with a ballot paper and vote.
Officials had apparently been forced to authorise the ballot paper because they were not able to challenge her identification.
The Electoral Commission said in cases such as these, officials were advised to warn the voter they could potentially be committing a criminal office.
The Lib Dem candidate in Birmingham Ladywood Ayoub Khan - who lost to former Labour Cabinet minister Clare Short by 6,801 votes - said "personation" had been happening in the constituency.
Although he conceded the alleged irregularities would have made no difference to the poll, he said the party was considering a challenge - which would have to be lodged in the High Court within 21 days.
"Polling agents have reported a degree of personation - people turning up to cast votes who are not the actual voter.
"We believe there may have been substantial fraud. That needs to be investigated."
The city's returning officer, Lin Homer, said Mr Khan's concerns had yet to be brought to her attention, but pledged that any matters raised would be thoroughly investigated.
And hundreds of voters in the London Borough of Hounslow were prevented from voting because of "clerical errors" in the electoral register.
The mistakes, which affected two constituencies Brentford and Isleworth and Feltham and Heston, were discovered too late to be corrected before polling day.