EU referendum ballot paper
More than 500,000 registered to vote on the government website on the deadline day of 7 June Getty/AfP

Labour leader Jeremy Corbyn is among a number top politicians calling for the government to extend its deadline for voter registration in the EU referendum. The move comes after a last-minute rush on the government website caused the page to crash around 10pm BST, potentially leaving thousands of potential voters without a say in the 23 June ballot.

"We became aware of technical issues late on Tuesday night due to unprecedented demand," a spokesperson for the Cabinet Office said.

"Some people did manage to get through and their applications were processed. We tried to resolve the situation as quickly as was possible and to resolve cases where people tried to register but were not able to."

But Corbyn took to social media site Twitter to vent his frustration, while Liberal Democrat leader Tim Farron branded the situation a "shambles".

He added: "It is also a major blow to the 'In' campaign and our prospects of staying in Europe. With individual voter registration, and a big campaign to encourage young people to register, many of whom have been trying to do so last minute, this could have major consequences for the result.

"Evidence shows younger people are overwhelmingly pro-European, and if they are disenfranchised it could cost us our place in Europe. It could also turn them off democracy for life. Voters must be given an extra day while this mess is sorted out urgently."

The Scottish National Party (SNP) have also backed an extension. The party's cabinet spokesperson, Tommy Sheppard MP, said: "The government must extend the deadline for voter registration for the EU referendum – nobody should be denied their opportunity to vote.

"The time for incrimination – and to ensure this never happens again – will come later. The urgent priority is to extend the deadline and ensure that everyone has the chance to exercise their democratic right."

More than 500,000 people registered to vote on 7 June, with just over a fortnight to go before the EU referendum. The latest opinion poll from YouGov, of more than 2,000 people between 5 and 6 June, put Remain one point ahead of Leave (43% versus 42%), with 11% of respondents undecided.

UPDATE: The Electoral Commission has advised the government to extend its voter registration deadline.