The government's 'Register to vote' website was fully operational as the deadline to take part in the June 23 EU referendum passed at midnight on Thursday.
According to a live monitoring site there was a flurry of activity on the registration service webpage in the minutes before midnight.
The monitor showed there were just under 5,000 people using the service at 11.55pm and more than 3,000 still on the site after the deadline had passed.
This week emergency legislation allowing registration to continue until midnight on Thursday was passed by both the Commons and the Lords without a vote.
The measure to extend was rushed through after the registration website crashed hours before the original deadline of midnight on Tuesday, leaving thousands of people unable to submit their applications.