The Senior Counsel for Drs Katherine Zappone and Ann Louise Gilligan told the High Court today that, if the State bars partners in a same sex couple the right to marry the person they love, there was a prima facie case for discrimination.

Mr Collins was giving the opening address in the landmark case being taken by Drs Zappone and Gilligan for recognition of their Canadian marriage.

He said discrimination on the grounds of a range of 'suspect categories', including sexual orientation and gender, was already prohibited in Irish statutory law and in jurisprudence.

This is a landmark case taken by the lesbian couple to have their Canadian marriage recognised in Ireland.

Lawyers for Dr Katherine Zappone and Dr Ann Louise Gilligan say their case raises a fundamental question about the nature of marriage itself.

Dr Zappone, a public policy research consultant, and Dr Gilligan, an academic, met in Boston, Massachusetts and have been living together since 1981. They married in Canada in 2003.  Now they want the State to recognise that marriage.

They took legal proceedings after the Revenue Commissioners refused to recognise them as a couple for tax purposes.

Their lawyer argued the case was not just about maximising tax benefits but about the nature of marriage itself.

Senior Counsel Michael Collins said Drs Zappone and Gilligan were not arguing for any extra or special rights. They were arguing for the same right everyone else has - the right to marry a person of your choice who you love, the court was told.

He said the State was discriminating against the couple on the basis of gender and sexual orientation. And he said there were no public policy grounds sufficient to warrant the withholding of the right to marry from them. The case is expected to last around three weeks.