By Kylie MacLellan
LONDON (Reuters) - Britain will extend the voter registration period for its June 23 referendum on EU membership by 48 hours after a late surge in applications crashed a key website shortly before the Tuesday night deadline.
More than a million potential voters applied to register online over the last week, half of them on the final day, the government said, with a peak of more than 200,000 per hour ahead of the previous deadline of midnight (7 p.m. ET) on Tuesday.
Turnout is expected to be important in determining the outcome of the close-fought referendum, with young people considered to be more pro-EU but also less likely to vote. More than half of those who registered on Tuesday were under 34.
Some pollsters and analysts expect a high turnout to favor an "In" vote.
Matt Hancock, a minister in the government department responsible for registration, said on Wednesday the government would legislate to extend the deadline.
"We think it is right to extend to midnight tomorrow (Thursday) to allow people who have not yet registered time to get the message that registration is still open and get themselves registered," he said in a statement.
Hancock said on Twitter that the legislation, which opposition parties earlier had said they would support, would be brought to parliament on Thursday.
Several senior politicians and the Electoral Commission watchdog had earlier called for the deadline to be extended.
The Commission is planning for turnout of around 80 percent, well above the 66 percent seen in last year's national election, Chair Jenny Watson told Sky News.
Earlier, Hancock told parliament there had been problems with the website in the final two hours before the deadline due to record levels of users. It is not known how many people had tried and failed to register before midnight, he said.
The problems come after the Electoral Commission said last week a small number of EU citizens had mistakenly received notification they were registered to vote in the referendum but would not be allowed to do so.
The Guardian newspaper also reported thousands of postal votes from Britons in Germany may have got lost in the post after confusion about the type of pre-paid envelope supplied.
With polls showing Britons are evenly split, a narrow win for "In" could result in pro-Brexit campaigners questioning the way the referendum was conducted.
Bernard Jenkin, a pro-Brexit lawmaker in Prime Minister David Cameron's Conservative Party, said the deadline was set because the register had to be formalized and published before the vote.
"Any idea of rewriting the rules in a substantial way would be complete madness and make this country look like an absolute shambles," he told Hancock during an exchange in parliament.
"Will he bear these things in mind or risk judicial review of the result?"
(Additional reporting by Estelle Shirbon and William James, Editing by Stephen Addison)