The Cabinet Office is in talks with the Electoral Commission about the technical fault that prevented people registering to vote in the EU referendum.
The gov.uk website for voter registration crashed last night at around 10.30pm, in the final hours before the midnight deadline.
The government said the crash had led to “many” people being unable to register.
The Electoral Reform Society and a number of opposition MPs, including Labour leader Jeremy Corbyn and Liberal Democrat leader Tim Farron, have called for the deadline to be extended.
Farron said: This is a shambles the government has presided over and people must be given an extra day to exercise their democratic right.”
He added that it was “a major blow to the ‘In’ campaign and our prospects of staying in Europe”. This is likely because statistics have indicated that younger voters are more likely to register later, and they are more likely to be Remain voters.
The Cabinet Office said: “We are urgently considering what the options are for those who were unable to register to vote last night.”
It added that it was talking to the Electoral Commission and “provide an update as soon as possible”.
Commenting on the crash, Michael Allen, solutions vice principal at digital performance firm Dynatrace, said it was “vital” that organisations provide seamless user-experience when they use their websites.
“If that website is likely to experience peaks in demand, at times when it’s critical for your audience to have access, then you need to be confident that it can handle the extra traffic,” he said.
Allen added that there were lots of ways to manage this, from load-testing in advance to assessing how the site performs under high traffic.
“These measures really aren’t a luxury – they’re a necessity, as last night’s outage all-too clearly reminds us.”
Meanwhile, Toby James, a researcher who focuses on electoral participation said in his blog that the best way to avoid such problems was to use automatic registration.
“Such a situation is entirely avoidable,” he wrote. “In many democracies around the world, automatic registration is used to avoid a last minute administrative challenge. Why set ourselves up for a fall?”