Leave campaigners have been angered by the decision to extend the deadline to register to vote in the EU referendum.
The Government on Wednesday announced it had moved the registration cut-off back by 48 hours, until midnight on Thursday, on the advice of the Electoral Commission.
The move comes after the voter registration website crashed just two hours before the previous deadline of midnight on Tuesday.
Matthew Elliott, the chief executive of Vote Leave, claimed the extension of the deadline was linked to an attempt to stuff the electoral rolls with as many Remain supporters as possible.
“They’ve just told the House of Commons that their website crashed last night because of the high demand, but we know that the Government and their allies are trying to register as many likely Remain voters as possible,” he said.
Meanwhile The Spectator magazine reports that “senior figures” on the Leave side believe the registration website was “deliberately” crashed.
They reportedly believe the spike in traffic seen at 10.15pm on Tuesday is improbable in scale.
Leave.EU, another campaign to leave the European Union, is also reportedly threatening legal action over the extension of the vote, according to the Financial Times newspaper.
That group of campaigns previously threatened legal action when its rival Vote Leave was designated the official "Out" campaign. The threat was ultimately withdrawn.
Conservative eurosceptic MP Bernard Jenkin told the House of Commons today that any major extension could be open to legal challenge and would be "absolute madness".
"May I advise the Minister that it is probably legal to keep the site open for a short period - a few hours, to capture those who did not have the opportunity to register yesterday—but any idea of rewriting the rules in any substantial way would be complete madness and make this country look like an absolute shambles in the run-up to the referendum, which is such an important decision?" he said.
"Will he bear those things in mind, or risk judicial review of the result?"
At 10.15pm on Tuesday there were more than 50,000 users simultaneously accessing the voter registration website at any one time and attempting to sign up before the deadline.
People trying to register reported errors and timeouts as the original midnight deadline for eligibility to vote in the 23 June referendum approached.
Gloria De Piero, Labour’s shadow minister for Young People and Voter Registration, said the Leave campaigners were indulging in conspiracy theories.
“Vote Leave’s outrageous suggestion that enabling people to register to vote who were unable to do so through no fault of their own is a conspiracy, or ‘gerrymandering’, shows just how desperate they are,” she said.
“Anyone involved in politics should want as many people as possible to have their say in a decision that will have a profound and lasting effect on the future of our country. It’s called democracy”
Hundreds of thousands of people have signed up on the voter registration website as the deadline neared after an advertising and social media drive to get them to sign up.
Public statistics suggest most of the people signing up are relatively young – likely to be good news for the Remain campaign, which has been able to count on youth support in polls.
A disproportionate number of young people signups is to be expected, however, because older people are less likely to move house and more likely to be on the register already.
On Tuesday, the Vote Leave campaign was accused of using "underhanded tactics" after it used a Google advert to place its own website above the official voter registration page.
That website appeared to instruct people to "register to vote now", but in fact simply harvested the details of people who used it. It did not register them to vote.
As of later this afternoon, the website has been taken down. Vote Leave have not responded to requests for comment.
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