A series of polls have indicated that Ireland is very likely to vote in a favour of legalising same-sex marriage in an upcoming referendum.

Polls on Saturday suggested that voters would back the move in a referendum set for Friday by a margin as much as two-to-one, making Ireland the first country to approve the policy in a national plebiscite.

Support for homosexual rights has surged in Ireland, which has been considered one of the most socially conservative countries in western Europe, in recent decades as the power of the Catholic Church collapsed in the wake of a series of child abuse scandals.

The Irish Times poll of 1,200 voters showed 58 percent planned to vote in favour of the measure compared to 25 percent against and 17 percent undecided.

Two more polls to be published in newspapers on Sunday put support for the constitutional change above 60 percent.

Long considered a taboo in a country that only decriminalised homosexuality in 1993, gay rights have been championed by most of the country's main political parties.

Ireland's Prime Minister Enda Kenny was widely praised for appearing at a prominent gay bar last year at an event for gay members of his Fine Gael party.

The campaign has led to a number of high profile figures announcing their homosexuality publicly, including the country's health minister and prominent television journalist. 

In letters published on Saturday, a number of Catholic bishops, who have played a low key role in the campaign, warned their parishioners that the vote could profoundly change the understanding of marriage, family and parenthood.

Following suit

If Ireland votes yes, it will join 18 countries which have made, or are in the process of making the change, 13 of them in Europe.

Referendums have previously been held in Croatia and Slovenia, and in both cases voters rejected legalising gay marriage.

In Slovenia same-sex marriages were, however, legalised by parliament in March 2015.

The Netherlands became the first country to allow gays and lesbians to marry in a civil ceremony and adopt children while Belgium legalised same-sex marriage in June 2003, with some restrictions.

Spain's socialist government made same-sex marriage legal in July 2005, and homosexual couples were also allowed to adopt, regardless of their marital status.

In Norway, homosexuals and heterosexuals were put on the same legal footing in January 2009 and allowed to marry, adopt and resort to assisted reproductive technologies.

Other European countries that have legalised gay marriage include Iceland, Denmark, France, Luxembourg, and Finland. The UK legalised same-sex marriage in England and Wales in 2013. 

Source: Agencies