Thousands of people were left unable to register to vote ahead of the original deadline at midnight last night after a government website crashed due to the volume of traffic.
Opposition parties and the Electoral Commission had called for an extension to the deadline, and the Prime Minister earlier urged unregistered voters to continue to sign up using the website.
Emergency legislation will now be rushed through the Commons on Thursday to allow those registering late to vote in the referendum on June 23.
There were 214,000 people on the electoral registration site between 9pm and 10pm on Wednesday night.
It is not clear how many missed out when the website crashed just under two hours before the midnight cutoff, but it is understood that thousands may have failed to register in time.