(CNN) A campaigner has lost a court of appeal challenge after calling for gender neutral passports to be introduced in the UK.

Christie Elan-Cane was urging the Home Office to allow an "X" gender option , alongside male and female. They had argued the UK's current passport process is "unacceptable," and breaches international human rights law.

Elan-Cane's original legal challenge was rejected last year by London's High Court, and on Tuesday senior judges dismissed the appeal.

"I regret to inform that the Appeal Court has ruled in the UK government's favor in a judgment handed down this morning," Elan-Cane said in a statement on Twitter Tuesday, adding that they intended to seek permission for the case to be heard at the Supreme Court, which is the final court of appeal in the UK.

A handful of countries, including Germany, Australia and Canada, already offer a third option, other than male or female, on their passports.

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