Up to 40,000 Irish citizens living abroad are being urged to return home to cast crucial votes in a historic referendum in May that could overturn the country’s ban on abortion. A campaign, Home to Vote, is calling on the Irish diaspora in the UK, Europe, north America and elsewhere to book flights and ferries to Ireland to exercise their democratic right.

Three years ago thousands of Irish citizens returned home to vote on same-sex marriage legislation, boosting the remarkable two-thirds majority for changing the law. Campaigners now hope to repeat the feat.

More than three-quarters of a million Irish-born people live in other countries – a significant number set against the resident population of 4.8 million. Only those who have been abroad for 18 months or less and intend to return to Ireland are eligible to vote. Those qualifying must register in advance and vote in person.

The referendum will ask whether article 40.3.3 of the Irish constitution – known as the eighth amendment – should be repealed. This gives a foetus the same rights to life as a pregnant woman, and has been in place since 1983, enshrining in the constitution a ban on abortion, even in cases of rape and fatal abnormality of the foetus.

If it is overturned in a referendum expected on 25 May, legislation giving women an unrestricted right to abortion up to the 12th week will be introduced. Since 1983 an estimated 170,000 Irish women have travelled to the UK to terminate their pregnancies, incurring high costs, logistical difficulties and emotional strain. In addition, up to 2,000 women a year end pregnancies by taking the abortion pill, illegally obtained online.

No one under 52 has had a chance to vote on this before. It’s a once-in-a-generation opportunity Cara Sanquest, campaigner

Polls have shown a majority in favour of repeal, especially among young people, who form the majority of recent emigrants. The referendum is seen as another litmus test of liberalising social attitudes in Ireland and the declining influence of the Catholic church. “Lots of people have already pledged on Twitter to come home, saying they are booking annual leave and saving money for fares,” said Cara Sanquest of the London-Irish Abortion Rights Campaign, which is spearheading the effort.

“There is a huge Irish population in London but this is a global call for people to have their say in shaping the future of Ireland, a place where many will return to live at some point. No one under 52 has had a chance to vote on this before. It’s a once-in-a-generation opportunity. We’re asking people to make a journey in reverse that thousands of women are forced to make every year to have abortions.”

The Home to Vote website advises Irish citizens abroad of their rights and suggests ways of helping the campaign for those ineligible to vote. It also plans to raise funds for those struggling with travel costs.

Lianne Hickey, 26, who has been living and working in London for the past five months, has already booked flights and time off work. “Every vote counts, but it’s also important to send a message that Irish people want a fairer, safer world for Irish women, and are prepared to travel home for that,” she said.

“The referendum is just a recognition of reality: 11 women a day are forced to travel. We need to remove the shame and stigma, and allow women who need it to have a safe procedure in a familiar environment.”

In May 2015, Irish citizens travelled from as far as Australia to cast their votes in the equal marriage referendum. Hundreds posted pictures and accounts of their journey on social media under #HomeToVote, the same hashtag being used in the 2018 campaign.