The Government is being urged to hold an inquiry after potentially thousands of EU citizens and British expatriates were left unable to vote in this week’s European elections.

Campaign group the3million, which represents EU citizens in the UK, said it had received several hundred messages from people claiming they had been blocked from voting due to administrative errors by British councils.

Meanwhile, a number of British voters reported problems voting from EU member states, due to delays in receiving postal votes from UK councils.

Labour MEP Claude Moraes wrote to Home Secretary Sajid Javid on Thursday, calling for an inquiry into the “disenfranchisement of voters in a national election in the United Kingdom”.

He said councils had made three “main clinical errors” that appeared to have contributed to the issues: failing to communicate about the forms, failing to send the forms to people on time, and failing to register the forms when they were received.

Helen Thompson, a prospective Liberal Democrat parliamentary candidate in Lambeth, claimed the problems were “horrific”, estimating as many as 2,000 people may have been turned away in the London borough alone.

“If the pattern is repeated across the borough and London that could potentially mean thousands of votes for Remain parties not being cast,” she told the Press Association.

Lib Dem MEP Catherine Bearder also raised concerns on behalf of British expats.

In a cross-party letter to the Electoral Commission, she said: “We have received a number of complaints from these citizens who have been prevented from voting given the delays in their postal vote being sent by the local councils.

“Local councils have admitted that they were unable to print and send off postal ballots for the EU elections given the short time frame, which has left numerous UK citizens disenfranchised.

“This has left people’s voices silenced and is an affront to our democracy. We would like to request that you allow all postal votes received before the count on Sunday to be considered valid given that it is still within the EU election period.”

On Thursday, the UK’s election day, many complained on social media using the hashtag #DeniedMyVote.

In a statement, the Electoral Commission blamed “very short notice from the Government of the UK’s participation in these elections”.

EU citizens must transfer their vote from their member state to the UK by handing in a form 12 working days in advance of the poll, a process the Electoral Commission said “could be made easier”.

Claudia Falcone, 27, had sent her additional EU Parliament voter registration form after discovering it on social media, and rang the council to confirm she was on the register, but was also initially denied her vote.

“When I went to vote, the two clerks showed me that my name was on their list, but with ‘not allowed’ written next to it,” the PhD student from Germany, now living in Bangor, Wales, told the Press Association.

The3million said it is speaking with lawyers and called on whoever replaces Theresa May to “have a serious conversation about who can vote in this country”.

Co-founder Maike Bohn told the Press Association: “Leaving long-term non-UK residents out of the fundamental process of voting will hinder integration – something those who voted Leave said was an issue with immigration.”