Following the mayor of Milan’s promise of a register of gay civil unions, the Catholic Church has warned it could legitimise polygamy.

Giuliano Pisapia is backing the move to introduce the register of de facto couples as Italy has no national system for the legal recognition of gay relationships, the only remaining country in western Europe to operate without such a system.

The Belfast Telegraph translates his comments: “The establishment of a register of civil unions is aimed at recognising and protecting the rights of many couples in Milan and the rest of the country, couples that have been waiting too long for legal recognition.”

The register would be designed to afford some legal protections to gay couples who cohabit, but these would not be equivalent to marriage rights.

Alfonso Colzani, a spokesman for the Catholic diocese of Milan said in response there was a “risk that giving equal status to families based on marriage with those founded on civil unions will legitimise polygamy”.

He added: “Introducing a communal register of civil unions is an ineffective initiative – and maybe only a PR exercise. Instead it is the family that needs support in this time of hardship. The concept of marriage is a precise one and not to be confused with homosexual unions.”

Italian gay rights group Arcigay said of religious and political opposition to the plan that some in the city had shown “an incredible concentration of homophobia and prejudice”.