This five per cent could be as much as three million postal votes and there are suggestions that close results could be challenged in the courts over claims that legitimate votes were invalid.
In addition, new software systems designed to eliminate postal vote fraud have caused delays in some councils resulting in postal ballots being delivered late.
David Monks, head of returning officers, told the Times: "We have to reject many of them on grounds of mistakes rather than fraud. . . Many election officers are now asking why we are doing this, particularly …in areas with no history of fraud."
But Leeds city council, which received 80,000 postal vote applications from an electorate of 500,000, said none of the queried votes would be removed from the final count.
A spokesperson for the Department for Constitutional Affairs said any difficulties with software systems would not prevent postal voters from casting their vote and having it counted.
"It is important to remember that the majority of postal votes are received before polling day and will be checked and verified at opening sessions before polling day, so that on polling day itself the postal votes are ready to be counted," she said.
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