Internal Labour polls show the outcome of the same-sex referendum may be a lot closer than expected, the former Tánaiste Eamon Gilmore has said.

The polls conducted by the Labour party showed the vote would be tight and the polls low, Mr Gilmore said.

“The biggest danger is complacency,” he said.

“Don’t take the outcome of this referendum for granted. Ensure it passes. Don’t leave it to other people.”

The former Labour leader, who resigned after the party’s poor performance in European and local elections last year, said in 2012 the rights of gay couples to marry was “the civil rights issue of our generation”.

Mr Gilmore said if the same-sex marriage referendum was passed, it would have no implications on children.

“It’s essentially about saying to people that the love of a same-sex couple is no less valid that the love of any other couple,” he said.

The Dún Laoghaire TD said the referendum was about equality.

Mr Gilmore said the status of couples who are already married would not be changed.

He said the goal was not to reset marriage but extend the right to marry to same-sex couples.

Mr Gilmore told RTÉ radio the Government has received legal advice that to pass legislation for same -sex marriage would be "unconstitutional".