The extension to the EU referendum voter registration deadline could be challenged in the courts by Brexit campaign funder and businessman Arron Banks.
MPs vote today on emergency legislation to extend to midnight tonight the deadline to register to vote in the 23 June referendum – following a glitch which stopped people from registering online shortly before the previous deadline on Tuesday night.
But Mr Banks, who funds Leave.EU, accused the government of trying to “rig the referendum” and said he was considering seeking a judicial review.
Downing Street said the extension was “legally watertight”, but Mr Banks said it was an attempt to “load the dice” by adding more Remain voters to the register.
“For the Government to alter election law during an election period is absolutely unprecedented and unconstitutional,” he said in a statement.
“This isn’t some democratic initiative, it’s a desperate attempt by the establishment to register as many likely Remain voters as possible before polling day.”
Mr Banks said “terrific efforts have been made to target young people, thought to be more sympathetic to the EU”.
Polls show younger people are more likely to back remaining in the EU than older people, but they are less likely to vote.
Half a million people applied to register to vote on Tuesday, most of them online, but tens of thousands were prevented from applying that night after being hit by an error message.
There is a difference between applying to register and actually registering: previous elections have shown that many people applying to register are not added to the electoral register because their names are already included on it, but they have not realised this.
EU vote registration extended - desperate measures? Read Gary Gibbon's blog
Downing Street said 214,000 people were trying to use the registration website between 9pm and 10pm on Tuesday – before the glitch – but it was not known how many were prevented from registering before the midnight deadline.
Government figures show that of the half a million people registering to vote on Tuesday, 300,000 were under 34.
Despite Mr Banks’ concerns, Brexit supporter Michael Gove, a major player in the Vote Leave campaign, said he supported an extension on the basis that “the more people who register to vote on 23 June the better”.
The Leave campaign was boosted by the support of JCB Chairman Lord Bamford, who told his 6,500 staff in a letter that they should not fear an EU exit.
But it was hit by the defection to the Remain campaign of Tory MP Sarah Wollaston, who said she was quitting Leave because she doubted its figures.
Dr Wollaston, chairman of the Commons health select committee, said its claim that leaving the EU would mean £350m a week more for the NHS was untrue.