A woman enjoys a beer outside The Anglesea Arms which has been turned into a polling station for the European elections, taking place despite Brexit uncertainty, in London, Britain, May 23, 2019. REUTERS/Henry Nicholls

LONDON (Reuters) - Hundreds of EU citizens trying to cast their vote for the European Parliament elections in the United Kingdom on Friday have been turned away because of administrative mistakes, a campaign group said.

Britain was not supposed to be taking part in the elections for the European Parliament as it was due to leave the bloc on March 29. However, the rejection of the divorce deal that Prime Minister Theresa May struck with Brussels meant Brexit was delayed until October, requiring the vote to go ahead.

Large numbers of EU nationals recounted on Twitter how they had arrived at polling stations to find their names had been crossed off the list of eligible voters, saying officials had failed to deal with the necessary forms in time.

“I’m an EU citizen and registered to vote in time, but apparently my form saying that I was going to vote in the UK didn’t arrive before the deadline,” said Ana Clara Paniago.

The UK’s election watchdog said if an EU citizen wanted to vote in Britain rather than their home state, they had to transfer their right to do so 12 days ahead of the poll.

“We understand the frustration of some citizens of other EU member states, resident in the UK, who have been finding they are unable to vote today when they wish to do so,” the Electoral Commission said in a statement.

“The very short notice from the government of the UK’s participation in these elections impacted on the time available for awareness of this process amongst citizens, and for citizens to complete the process.”

The 3million group, which campaigns in Britain on behalf of EU citizens from the bloc’s other 27 member states, said it had been contacted by hundreds of angry people who had been turned away when they tried to vote.

“It is outrageous that the incompetence and unwillingness of the government and the Electoral Commission have denied these people a vote,” it said in a statement, calling for an investigation into what it called a “democratic disaster”.