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. The hashtag #DeniedMyVote began trending in Britain as voters cast their ballots in one of the 28 countries taking part in four days of voting. "Early morning visit to cast my vote only to have it disenfranchised because my declaration that I wouldn't be voting in Sweden [my country of citizenship] hadn't been processed in time," Twitter user Lina Dencik wrote.

The lobby group, The3Million, representing the interests of EU nationals working and living in Britain said it had been contacted by "hundreds" of people who were turned away. "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." Britain's Electoral Commission said it was monitoring the situation but refused to take the blame.

Prime Minister May's government only acknowledged on May 7 that Britain will have to take part in the European election because it had not been able to complete the Brexit process in time. This limited the time both EU and U.K. authorities had to explain the different voting rules each country has for its expatriates. The pro-EU Liberal Democrats accused May's government of deliberately trying "to silence the voices of our fellow Europeans." "Liberal Democrats will hold the government to account for this bureaucratic shambles," the party said in a statement.