Polygamy is bad for children and bad for women and the law upholding it ban is therefore constitutional, the Chief Justice of British Columbia Supreme Court has ruled.

In a decision yesterday, Chief Justice Robert Bauman found that the law banning polygamy is constitutionally sound.

Pro-marriage groups, have welcomed the ruling saying it recognises that marriage not just a private matter and has a social dimension.

The ruling stemmed from a failed prosecution in 2009 of two leaders of a breakaway Mormon sect in British Columbia.

The province of British Columbia had asked the court to review the law after polygamy charges against two men in the village of Bountiful were dropped in 2009 partly over concerns about the law’s constitutional status.

The sect in Bountiful, the Fundamentalist Church of Jesus Christ of Latter-day Saints, has links to the Yearning for Zion Ranch in Eldorado, Tex., where the authorities seized 468 children in a raid during 2008 and brought charges against 12 men.

The Royal Canadian Mounted Police said in February that they were conducting a criminal investigation in Bountiful because evidence presented to the Supreme Court suggested that eight girls from the village, some as young as 12, had been sent to the United States to marry men.

Members of the sect have argued that polygamy should be allowed under Canada’s constitutional guarantees for religious practices.

But Chief Justice Bauman attacked polygamy in strong terms.

“Women in polygamous relationships are at an elevated risk of physical and psychological harm,” Bauman said in his 357-page ruling.

“They face higher rates of domestic violence and abuse, including sexual abuse.”

He added: “Early marriage for girls is common, frequently to significantly older men. The resultant early sexual activity, pregnancies and childbirth have negative implications for girls, and also significantly limit their socio-economic development.”

But he said minors in polygamous relationships should be exempt from prosecution under the polygamy section of the Criminal Code. He suggested the legislation be “read down” to exclude children between 12 and 17.

In a statement, Dave Quist, Executive Director for the Institute of Marriage and Family Canada welcomed the ruling saying that the practice of polygamy institutionalised “patriarchal domination, gender inequality and a host of other negative behaviours”.

He said: “Conversely, research shows that two-person, man-woman marriage is the strongest family form, bringing a host of physical and emotional health benefits to children and the adults involved.

“Oftentimes we are led to believe that our relationships are only private matters. This ruling shows this is not the case, given the radically different outcomes associated with polygamous marriage as compared with other family forms, outcomes which affect the way we live.

“This sends a strong message across Canada that further changes to the institution of marriage are deleterious to society and should not be entertained.”