A US federal court has upheld a ruling by a gay judge that California’s ban on gay marriage is unconstitutional.

This is the latest round in a long legal battle over the issue.

US District Judge Vaughn Walker ruled in August 2010 that the ban should be lifted. In the following months, it emerged that he was gay and in a long-term relationship.

Opponents of gay marriage complained that as a gay man, he had a conflict of interest. They claimed he planned to marry his partner but could show no evidence for this.

Chief US District Judge James Ware ruled yesterday that the fact Judge Walker is in a relationship would not make him “so interested in marrying the person that he would be unable to exhibit the impartiality which, it is presumed, all federal judges maintain”.

The ruling means gay marriage campaigners in the state are one step closer to reaching their goal.

After Judge Walker’s ruling last year, opponents applied – and won – a stay while they appealed the decision.

The 9th US Circuit Court of Appeal is currently considering that decision but says it will not make a ruling until the state Supreme Court rules on whether gay marriage opponents have the legal standing to appeal the original judgement.