Heterosexual couples in France are opting for civil unions over marriage.

The country allows both straight and gay couples to have PACS, or pacte civil de solidarité, although gay couples cannot marry.

However, the civil ceremonies have become increasingly popular for straight couples and there are now two PACS for every three marriages, the New York Times reports.

PACS became legal in 1999 and in 2000, 75 per cent of agreements were between straight couples. Last year, this rose to 95 per cent.

Just 250,000 couples married in France last year but 173,045 had PACS. If trends continue, PACS will soon overtake marriage.

PACS require a short court appearance to enact and can be ended by registered letter.

They offer most of the rights and benefits of marriage but are said to be popular with young couples wishing for lighter taxes, or those who dislike the traditional connotations of marriage.

In the UK, only gay couples can have civil partnerships and only straight couples can marry.

Civil partnerships offer almost all of the rights of marriage, although partners cannot have a religious ceremony.

Next week, gay and straight campaigners are to launch a legal bid to give all couples the choice of between the two institutions.