Three people living together in a polygamous union must be allowed to have family rights and a formalised civil union, a Brazilian notary has argued.

The Rio de Janeiro trio, an anonymous man and two women, having been living together three years, sharing bills and a bank account and otherwise acting like a married couple, according to the BBC.

Sao Paulo's public notary Claudia do Nascimento Domingues said the three had a formalised union three months ago, and that they should be entitled to family rights.

The union, she said, was just a new, modern kind of family. "We are only recognising what has always existed. We are not inventing anything.

"For better or worse, it doesn't matter, but what we considered a family before isn't necessarily what we would consider a family today."

Domingues said nothing existed in Brazilian law to prevent family rights being shared by more than two people.

Nathaniel Santos Batista Junior, a jurist who helped draft the civil union, told Globo TV that the couple wanted to protect their rights in case of separation or death of a partner.

He said the document was not the same as a marriage.

Brazil's Commission for the Rights of the Family within the Institute of Lawyers, has said the union will not be allowed to remain in place.

Brazilian psychologist and evangelical Christian, Marisa Lobo, who has been known to promote "gay cures" in the country, expressed shock in a piece for the Verdade Gospel.

She said: "Jesus, come back soon! My question is: what are these law holders playing at? What is the media playing at?

"What are these groups playing at by confronting the society with totally distorted values.

She claimed an employee of Domingues had confided in her about their discomfort with the union: "I try to imagine the sons of these three people, how would they feel?

"But today everything is like this, we are even afraid to talk about it."

The legal status of polygamy varies, and it is accepted in nearly fifty countries worldwide, mostly Muslim or African states.

The UK accepts polygamous unions if they have been performed in countries where it is legal, and partners are allowed only strictly limited welfare benefits, and the marriages cannot be performed in the UK.

Polygamy is legal in Australia, one of the only Western nations to permit it, but only when the union is based around religious or cultural marriage - and it is commonly practiced among the Aboriginal population.