A record-breaking 469,000 people registered to vote online in one day for the 2015 general election - as the deadline closed on 20 April.
Web registration reached a peak at 20:05 when 18,372 added their names to the electoral roll - five minutes after Ed Miliband was interviewed on the BBC.
A further 16,000 people filled in paper registration forms.
The deadline for postal vote applications is 17:00 BST. The proxy vote deadline is 17:00 BST on 28 April.
Of those who used the online system Gov.uk on Monday, 152,000 were aged 25 to 34, 137,000 aged 16 to 24 and 89,500 were 35 to 44.
Alex Robertson, the Electoral Commission's director of communications, said: "It's absolutely fantastic to see that over the last few weeks, over two million people have applied to register to vote, with a huge surge of numbers yesterday.
"On the day of the deadline we saw almost half a million people apply to register in just one day - the busiest day since the introduction of the new online system."
The Electoral Commission said there have been 2,296,530 online applications to register to vote since its campaign began on 16 March. Of these, 707,171 applications were made by 16-24 year olds.
The previous record for single day sign-ups was 166,000 on 5 February - National Voter Registration Day. The third highest was 123,000 online applications on Sunday, 19 April - following David Cameron's appearance on BBC's Andrew Marr show. The next highest was 110,000 on Thursday, 16 April - the day of the BBC's live election debate featuring the leaders of the five main opposition parties.
Research carried out in 2014 suggested that 7.5 million people eligible to vote were not on the electoral register.
The UK general election takes place on 7 May. Local government elections are taking place across England - excluding London - on the same day. A number of mayoral elections are also taking place.
As registration records are managed on a constituency basis, it will not be known how many people signed up to vote until after the election.
The last general election in 2010 saw a voter turnout of 65.1% across the UK, an increase on the two previous elections in 2005 and 2001 when turnout was 61.4% and 59.4% respectively.
The 2001 election was the first time since World War Two that turnout had fallen below 70%.
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