Campaigners for a No vote in the marriage referendum say the head of the Referendum Commission has contradicted himself.

Mothers and Fathers Matter claim there is a contradiction between comments Mr Justice Kevin Cross made on radio today, and in a newspaper interview last week.

Today he said surrogacy was not an issue in the referendum - but last week discussed how it would be "difficult but not impossible" for the Oireachtas to pass laws giving preference to straight couples.

Mothers and Fathers Matter legal advisor Tom Finegan says if surrogacy was not a factor, Mr Justice Cross would not have had to make his comments last week.

While politicians supporting the Yes vote have again insisted surrogacy has nothing to do with the referendum debate.

Fianna Fail justice spokesman Niall Collins says concerns about surrogacy in Ireland are a "red herring" which the public should not buy into.

Mr Justice Kevin Cross told Newstalk last week that there is no automatic right to have children, no automatic right to adoption and no automatic right to surrogacy in Ireland - and that will not change regardless of the result on May 22nd.