Forcing non-gendered applicants to apply for either male or female passports is unlawful, the court of appeal has been told.

Opening a challenge to the Home Office’s refusal to provide gender-neutral, or “X”, passports to UK citizens, Kate Gallafent QC said it was a breach of their human rights. “The current passport system says [that applicants] must accept that they are either male or female,” she said.

The legal challenge has been brought by Christie Elan-Cane, a non-gendered activist who has campaigned on the issue for more than 25 years and given evidence to parliament about transgender equality.

Elan-Cane applied for a passport in 2010. “At that point the response was that the computer would not accept it,” Gallafent said.

Up to 1% of the population, about 630,000 people, may not identify as male or female, Gallafent told the court. No evidence had been produced to show the refusal was based on security considerations, the court was told.

Ten countries offer citizens gender-neutral travel documents. Australia, Canada, Denmark, Germany, Malta, New Zealand, Pakistan, India, Ireland and Nepal have a third category besides male and female. A number of US states, including California, New Jersey and Oregon, issue gender-neutral driving licences and birth certificates.

Standards for machine-readable passports set by the UN International Civil Aviation Organisation (ICAO) allow for individual states to enter M, F or X in the category indicating an individual’s sex, with X standing for unspecified.

More than 80 MPs signed the most recent Commons early day motion calling on the HM Passport Office and the government to make available X passports “to people who do not identify with a particular gender”. Jeremy Corbyn is among those who have signed earlier motions of parliamentary support.

Elan-Cane, 62, who was born female but began transitioning after surgery, believes individuals should be given more than the binary choice of being a man or a woman.

Human Rights Watch is intervening in support of the claim. The high court rejected the claim last year but permission to appeal was granted.

Critics say denying X passports to individuals whose identities are neither male nor female subjects them to a discriminatory policy, which forces them to declare an inappropriate gender.

Lawyers for Elan-Cane will also argue the policy is inconsistent, as border control officers allow holders of foreign X passports to enter the country at airports and ports.

Solicitors from law firm Clifford Chance as well as Kate Gallafent QC and Tom Mountford of Blackstone Chambers are working pro bono on the claim. They will argue that Elan-Cane’s human rights under articles 8 and 14 of the European convention on human rights – the right to private and family life and absence of discrimination – are being breached by the Home Office’s passport policy.

The court will be told that the Passport Office’s policy is ”forcing a [group] already marginalised within gendered society to collude in their own oppression/invisibility through a forced and unwilling self-denial of their identity in return for issuance of a UK passport”.

Speaking before the hearing, Elan-Cane said: “Legitimate identity is a fundamental human right but non-gendered people are treated as though we have no rights. 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.

“The UK government has consistently and consciously shown a determined unwillingness to accommodate non-gendered people’s legitimate needs. We are socially invisible and we are ‘inconvenient’ in a society where so much – even the legislative system – is bound and classified in accordance to gender. The government prefers to respond to our situation as though we do not exist rather than work towards enabling our assimilation into gendered society.”

The Home Office has argued that issuing passports with an X marker would have widespread implications and lead to additional costs across the whole of government. It would be a disproportionate burden, it maintains, since only a few people would benefit from the change.