In the run-up to the same-sex marriage referendum in May 2015, social media was flooded with stories of Irish emigrants returning home to vote. Journeys on planes, trains and ferries were documented at every stage of the trip with TV film crews greeting arrivals at Dublin Airport in what turned into a festival atmosphere.

On Thursday and Friday, there will another flood of emigrants back into the country, although this time campaigners are emphasising to returnees the legalities that surround voting in Ireland for those now living abroad.

“We saw how mobilised the voters were for marriage equality and we wanted to capitalise on that this time. We wanted to make sure that there is nothing that can call the referendum into question if we get a Yes vote.

“We wanted to make sure we had done everything in our powers to inform everybody and let people know who was eligible and how to register and make sure they have everything in place,” said Claire McGowran from the London Irish Abortion Rights campaign.

Under the 1992 Electoral Act, Irish citizens who have left Ireland for no longer than 18 months are still entitled to vote, though, in reality, many continue to receive polling cards at their last Irish address for far longer than that.

However, the 18-month rule is qualified. Ailbhe O’Neill, a barrister and lecturer at Trinity College, who was the legal adviser to two referendum commissions, said a person would not have given up their residence if they intend to move home within the 18-month timeframe after they have left the country.

“The key issue under the Act is . . . whether the person intends to return. For example, a person who moves abroad to study for a year but intends to return thereafter would not lose their status of being ordinarily resident under the Act, whereas a person who emigrates with no intention of returning within the timeframe would no longer be ordinarily resident,” said Ms O’Neill.

Population of 40,000

There are over 750,000 Irish-born people living abroad and it is estimated that those who can still vote number about 40,000, or so, according to research by the London Irish Abortion Rights campaign.

Awareness of the 18-month rule has been limited, said Ms McGowran. “The amount of people who were shocked to hear about the 18-month thing was quite startling. I think because of that it became apparent that we had to do a lot of awareness around [the issue],” she said. “Our big point in all of this is not to have an issue after the referendum and that if we get a yes it is very fair and clear.”

London-based Jane White: “Lingering uncertainty makes it all the more important for those of us who are eligible to vote and can afford to travel home to go back and ensure we make our votes count and vote to repeal.”

Jane White (31), who works in advertising sales in London, examined the law after friends mentioned that they were no longer eligible to vote. “There are people in my life who still remain undecided and that lingering uncertainty makes it all the more important for those of us who are eligible to vote and can afford to travel home to go back and ensure we make our votes count and vote to repeal,” she said.

Aoife Cassin (26) from Longford has been living in Rome for the past 11 months and also intends to return to vote yes. “I was already aware Irish citizens living abroad had to travel home in order to vote, which I feel, like the Eighth Amendment, is also outdated,” she said.

Aoife Doran (21) from Dublin returned home in October to register to vote from Amsterdam, where she is studying. “I have been directing fellow skint students to the Abroad for Yes Facebook group, a wonderful page of solidarity and camaraderie. This group links up sponsors with those eligible voters hoping to return home to vote.”

Legal challenge

The issue of how many people are still on the register despite living abroad for over 18 months has led to suggestions that a legal challenge could be possible with a tight result.

Amsterdam-based Aoife Doran: “I have been directing fellow skint students to the Abroad for Yes Facebook group, a wonderful page of solidarity and camaraderie.”

Maintaining the electoral register and ensuring that it is accurate is the job of city and county councils. So far, there has not been a challenge to a referendum based on the validity of people being on the register. O’Neill said the courts are reluctant to interfere with the results of referendums as they are the will of the people. The Supreme court ruled in 2015 that only cases “with a real likelihood of resulting in a setting aside of a referendum result” should be given a full hearing.

However, reform of the register has been on the agenda for the last decade. A 2008 report by an Oireachtas committee found problems with accuracy, omissions and duplications due to varying levels of commitments in maintaining the data and insufficient staff to gather information. A 2016 committee report recommended that responsibility for reform of the electoral register should be transferred to the Electoral Commission.

While there will be a percentage of No voters among whatever number do come home to vote, Ms McGowran said it tended to be a younger generation who emigrated and there was more support for Repeal among 18-24 year olds.