A former Fianna Fáil minister says the marriage equality debate would be better served if political parties stayed out of it.

Pat Carey, who is gay, says he is concerned that the campaign by his own party on the referendum is lacking in energy and urgency.

The former minister for community, equality and gaeltacht affairs has admitted he has some regret about not coming out himself while in public office.

He also says he has great admiration for the Health Minister Leo Varadkar, who spoke publicly about being gay recently.

Mr Carey told the Pat Kenny Show here on Newstalk that while the campaign for marriage equality might benefit from a lack of political involvement, it is politicians who are best placed to run such campaigns.

It comes as Liberty Hall in Dublin is lit up in rainbow colours for the launch of a trade union led same-sex marriage campaign.

ICTU is supporting the 'Trade Unionists for Civil Marriage Equality' drive, ahead of the May referendum.

The Dublin Gay Men's Chorus will help to launch the campaign this evening, on the eve of Valentine's Day.

Ethel Buckley from the ICTU executive council explains why trade unions are campaigning for a Yes vote.

The former minister also said he thinks the next government will be a coalition between his party and Fine Gael and says he has been of that view since 2011.

It is reported today that Fianna Fáil is aiming to double its current 20 seats in the next election, targeting constituencies outside Dublin.