A vote is set to take place in the Republic of Ireland next week, giving citizens the opportunity to decide if same-sex marriage should be legalised.

Historically a conservative Catholic country, homosexuality was illegal in Ireland until 1993. The Civil Partnership Act was enacted by the Irish government in 2010 and the first partnership between two men registered the following February.

However, there have been growing calls for full equal marriage legislation, particularly in the wake of the UK's Marriage (Same-Sex Couples) Act 2013. The referendum on May 22 is therefore a source of great anticipation and tension across the country.

Who is for it?

Kieran Rose of the Gay and Lesbian Equality Network (GLEN), praised the referendum's announcement as "another historic step in the remarkable 20 year journey from gay law reform to full Constitutional equality for lesbian and gay people in Ireland". Irish Prime Minister Enda Kenny, who has campaigned for a 'yes' vote, recently said that it would "actually strengthen the institution of marriage because it extends it to more people" and insisted that it would not impose on religious freedom. "This vote will allow same-sex couples to receive full legal protections, and will not force any Church to recognise same-sex marriage. Importantly, marriage equality will not in any way affect the institution of marriage," he said.

All of the major political parties are calling for a yes vote.

Who's against it?

As expected, the referendum has faced significant opposition, particularly from the Roman Catholic Church. "The Bishops of Ireland are clear that they cannot support this amendment and they have asked the people of Ireland to reflect and pray very carefully before voting," Archbishop Eamon Martin, Primate of All Ireland, said yesterday. He also said that there are "no grounds for considering homosexual unions to be in any way similar or even remotely analogous to God's plan for marriage and family".

The Presbyterian and Methodist Churches have also urged Christians to vote no next Friday. "The Presbyterian Church in Ireland upholds the historic – and Christian – view of marriage as exclusively between one man and one woman. We affirm that it is needed for the common good of society," its statement read.

"A redefinition of marriage would establish new norms within our society, the implications of which have not been fully explored. We acknowledge that this is an intensely emotive subject and trust that all will engage in the debate with gentleness and respect as we approach the Referendum."

What's the likely outcome?

According to the most recent polls, around 75 per cent of the population is in favour of 'marriage equality'. That figure rises to 80 per cent for younger voters, with over-65s markedly less enthusiastic. However, a good number of young people – perhaps as many as 120,000 – aren't registered to vote, and have been the subject of massive get-out-the-vote campaigns. Supporters warn that the final result may be much closer than the polls indicate; pollsters have not been very accurate in past referendums and support has tended to be overstated.

What does it mean for the Churches?

Religion in Ireland is overwhelmingly Roman Catholic, and historically the Catholic Church has wielded huge influence. A relentless series of revelations about its conduct in various areas ranging from sexual abuse to the conditions in orphanages and homes for unmarried mothers has led to an evaporation of support; in 1984, nearly 90 per cent of Irish Catholics went to Mass every week, whereas by 2011 only 18 per cent did. For many Irish voters, the fact that the Church is opposed to something will encourage them to vote for it. If the vote in favour is as much as polls say, it will cruelly underline the Church's irrelevance.

How will the Church deal with it?

In practical terms, the Church has said that if the vote passes, it may no longer perform the civil elements of a marriage service, meaning that couples married in a Catholic ceremony would have to have a separate civil registration. However, the widespread support for gay relationships and the very public opposition of the Church has driven another wedge between the Catholic Church and what was once the most religious population in Europe.