A group of three senior lawyers has warned that a victory for the Yes vote campaign in the same-sex marriage referendum would lead to same-sex couples having the same rights as heterosexual couples to use surrogacy and assisted human reproduction.

The group say that the chairman of the Referendum Commission, Mr Justice Kevin Cross, has said it would be difficult to imagine the legislature privileging an opposite-sex couple over a same-sex couple, where accessing surrogacy services is concerned.

The lawyers concerned about the effects of a Yes vote are William Binchy and two senior counsel, Patrick Treacy and Shane Murphy.

In a statement they say that a female homosexual couple can only procreate with donor sperm and a male homosexual couple would require a donor egg and a surrogate mother.

They say there is a strong argument that these practices will enjoy constitutional protection if this referendum proposal is passed.

They say the Government intends to enact a surrogacy bill which will provide for surrogacy in accordance with the new constitutional right of two married men to procreate.

The lawyers say Mr Justice Cross has said it would not be impossible, but it would be difficult to imagine the legislature privileging an opposite-sex couple over a same-sex couple where accessing surrogacy services is concerned.

Former Minister for Justice, Alan Shatter, has dismissed the groups's claim as a red herring saying neither surrogacy nor assisted human reproduction are relevant to the referendum.

Alan Shatter, a leading advocate of a Yes vote, wants Senator Rónán Mullen to explain why, last March he told the Seanad debate on the Family Relationships Bill that "failure to ban egg and sperm donation in the Children and Family Relationships Bill is a big mistake."

Speaking to RTÉ News Mr Shatter said "we have many couples in Ireland who have suffered fertility issues who for the last 30 years, through assisted reproduction, have had children- children loved by them- by their grandparents."

"Some of these are now adults who will be voting" he said.

He added "if Senator Mullen and others had their way not only would none of these children have been born, no couple in the future suffering fertility difficulties would be able to access assisted reproduction methods."

Yes Equality said it welcomed what it described as the legal clarity brought to the debate following Mr Justice Cross' comments.

Spokesperson Grainne Healy said statements by the commissioner and published in The Irish Times clarify that neither surrogacy or adoption have anything to do with the referendum.

Mr Justice Cross also said a Yes vote will not redefine what marriage is but it will redefine the view as to who can get married and same-sex couples will have the same constitutional status as heterosexual couples.

Ms Healy said civil partnership is a lesser, unequal and unprotected status and a Yes vote would provide gay people and their families with full constitutional equality.