A supporter of the anti-gay US group National Organisation for Marriage has claimed that banning gay marriage will save states money.

The claim, which goes against most credible research, was made by Tamara Scott, Iowa’s director of Concerned Women of America, at a rally in Des Moines this weekend.

She said that traditional families were being threatened by same-sex marriage, leading to costly social breakdown.

Generally, research shows that allowing same-sex marriage benefits states financially. California’s gay marriage trial heard earlier this year that if more gay people married, they would increase school district revenues, real estate, payroll and sales taxes and would be more likely to be insured.

Married people are more likely to be wealthier than their unmarried counterparts and a Williams Institute study last year said that if half of all US cohabiting gay couples married, this would boost the economy by about $9.5 billion (£5.8 billion).

There is also much research to show that allowing gay people to marry can empower them, lessening rates of mental ill health and providing better environments for their children.

But Ms Scott claimed that the economic downturn could be blamed on the social costs of “traditional families” being threatened by gay marriage, the Iowa Independent reports.

Citing a study from a Washington DC-based Christian group from 2009, she said: “It costs you, the taxpayer, as high as $280 billion a year for fragmented families, according to the Family Research Council.

“If we would correct the breakdown of the family by one per cent, we could save the taxpayer $3 billion a year.

“An easy fix and a better fix long term for our children… When the family is healthy, the community benefits. When the family is hurting, society will pay the cost one way or another. We can fix this economic downturn very easily by fixing some hearts.”

At a pro-gay marriage rally in Des Moines on the same day, the claims were rubbished by Iowa first lady Mari Culver.

Ms Culver told the newspaper: “Heterosexuals have not done a great job with marriage and the family. I think a strong middle class makes a strong economy. I think (NOM) is looking for some economic cover, rather than revealing that some in their group are simply anti-gay.”