(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.
"X" is accepted as a gender entry on machine-readable travel documents, alongside "M" and "F," under standards set by the International Civil Aviation Organization.
''Legitimate identity is a fundamental human right but non-gendered people are treated as though we have no rights," Elan-Cane said in a statement Tuesday. "It is unacceptable that someone who defines as neither male nor female is forced to declare an inappropriate gender in order to obtain a passport."
"This decision is devastating to me. It is bad news for everyone who cannot obtain a passport without the requirement imposed by the UK government that they should collude in their own social invisibility."
Clifford Chance, the law firm representing Elan-Cane on a pro bono basis, said that the court found the UK government's policy, which requires an "M" or "F" gender marker was not unlawful.
However, the court also held that the European Convention on Human Rights "guarantees a right to respect for non-gendered identity," the law firm added.
A spokesperson for the Home Office told CNN: "We welcome the Court of Appeal's judgment."