A witness appearing on behalf of supporters of California’s gay marriage ban told a court yesterday that allowing same-sex couples to wed would improve the well-being of their children.

David Blankenhorn of the conservative think tank Institute for American Values appeared as the defendants’ second and last expert witness in the trial on whether the gay marriage ban is constitutional.

He testified that he believed children were brought up best in a marriage between a man and a woman but conceded under cross-examination that children of gay parents would benefit if their parents were allowed to marry.

Blankenhorn said: “Adopting same-sex marriage would be likely to improve the well-being of gay and lesbian households and their children.”

Yesterday, he said that allowing gays to marry could undermine traditional marriage and lead to the legalisation of polygamy.

However, he also said the country would be “more American on the day we permit same-sex marriage than the day before”.

According to Reuters, some his remarks provoked sounds of surprise from gay couples in the courtroom.

The cross-examination of Blankenhorn marked the end of evidence in the San Francisco trial.

It will go on hiatus until Judge Vaugn Walker releases a date for closing arguments.

Proceedings were set to be broadcast on YouTube until a last minute decision from the Supreme Court barred this after gay marriage opponents argued they could be harassed and intimidated if proceedings were shown.

Today, gay equality group Courage Campaign said the trial was a “historic marker” in the struggle for lesbian, gay, bisexual and trans equality.

Chairman Rick Jacobs said: “Given the devastating testimony of defence witnesses, it is no wonder that ProtectMarriage.com wanted to keep cameras out of the courtroom.

“If their witnesses had been revealed to the public, Americans would have seen the Prop 8′s fear-mongering campaign exposed. The past 11 days of trial laid bare the truth about the Prop 8 proponents.

“The foundation of the Prop 8 campaign strategy was exposed, a strategy intentionally fuelled by lies and misinformation about gay men and lesbians.”