The appeal for an inquiry into the #DeniedMyVote election scandal also comes in what many predict to be a tumultuous week in the long-running Brexit saga, with an EU summit on Thursday and Friday due to sign off any proposal put forward this week by the UK Government.
Campaigners have garnered over 145,000 signatures on a petition after the UK’s Electoral Commission last week published a damning report on the way the EU elections were conducted amid claims that up to 1.7 million EU citizens and Britons abroad were denied a vote.
They have also written to the Council of Europe and submitted evidence to the European Parliament’s Brexit Steering Group calling for a "full investigation."
UK Labour MEP Claude Moraes and Greens deputy Molly Scott Cato have raised the issue with the Venice Commission of the Council of Europe.
With a cloud of uncertainty still hanging over the possibility of the UK crashing out of the EU on 31 October, a demonstration at the weekend again put the spotlight on the problems faced by EU citizens in the UK in May’s EU elections when many say they were turned away at polling stations.
This took place because hundreds of thousands of EU citizens had not completed a supplementary form that was required to be able to vote in the elections in the UK.
Some say they never received the form while others received it too late or sent it back but the form was lost by their local council.
"The [UK] elections to the European Parliament had major shortcomings and were not worthy of a modern democracy" Bob Posner, UK Electoral Commission
One campaigner, Roger Casale, a former Labour MP, said, "The reasons for this failure were many and varied but the consequences were the same - voter disenfranchisement and on a massive scale."
Thousands held a rally in London on Saturday to demand legal safeguards for citizens’ rights "in a post-Brexit Britain", including the right to vote in future elections.
The demonstration brought together a wide range of campaign groups including Final Say for All, Voices for Europe, In Limbo, Bremain in Spain and New Europeans.
Speakers included Danish-born UK resident Else Kvist, who said she was denied a vote in the elections.
Describing how she felt when she arrived at her polling station in Newham, London, and was told that she could not vote, Kvist said, "It was like a slap in the face. For me it was the last straw. I have lived here for many years. I have paid my taxes. I gave birth to my daughter in a British hospital and now she goes to a British school. When I couldn't vote, I felt I had been downgraded to a second-class citizen."
Bob Posner, chief executive of the Electoral Commission said, "The elections to the European Parliament had major shortcomings and were not worthy of a modern democracy."
Prior to the elections, campaigners raised the alarm with MPs, MEPs and with the UK Government Minister David Lidington.
"The Government’s systematic failure to prepare adequately for the European elections puts a stain on British democracy and a question mark over the outcome of the election" Roger Casale, New Europeans
They proposed remedial measures which could have been taken in time to prevent the mass disenfranchisement of EU citizens and Britons abroad but say these proposals were ignored by the Government.
Casale, of New Europeans, said, "The experience of Elsa Kvist and millions of other EU citizens in the UK may well represent a tipping point in the whole sorry Brexit saga."
"It is one thing to say you want to leave the European Union. But it is quite another to deny people their democratic rights at a time when the government should be doing everything possible to widen participation."
He added, "The Government’s systematic failure to prepare adequately for the European elections puts a stain on British democracy and a question mark over the outcome of the election."