A campaigner fighting for gender-neutral passports has urged the High Court to rule that the Government's current policy is "unlawful".
Christie Elan-Cane believes the UK's passport application process, which requires individuals to indicate whether they are male or female, is "inherently discriminatory".
Elan-Cane, who has campaigned for more than 25 years to achieve legal and social recognition for non-gendered identity, sees the issue of "X" (for unspecified) passports as a key focal point of the non-gendered campaign.
During a two-day hearing in London, Elan-Cane's lawyers will challenge the lawfulness of the policy administered by Her Majesty's Passport Office (HMP0), which is part of the Home Office, arguing that it breaches human rights laws.
Elan-Cane is present in court for the hearing before Mr Justice Jeremy Baker, who will also hear submissions on behalf of the Home Secretary that the case should be dismissed.
Kate Gallafent QC, for Elan-Cane, argued on Wednesday that the policy breaches the right to respect for private life, and the right not to be discriminated against on the basis of gender or sex, under the European Convention on Human Rights (ECHR).
She said: "For the claimant, obtaining and using a passport currently involves making a false declaration as to the nature of the claimant's gender identity, which causes the claimant considerable distress.
"The lack of a non-gender specific passport option impacts on the claimant's ability to obtain and use a passport on equal terms with persons who identify, and are identified, solely in terms of male or female."
She told the judge that the impact of the passport office's refusal to provide for X passports "affects not only non-gendered persons such as the claimant, but a broad section of the public" - including intersex and transgendered people and other individuals with gender dysphoria.
The policy requires Elan-Cane to "make a materially false declaration in respect of that core aspect of the claimant's human personality or to forbear from holding a passport".
She added: "If the claimant makes such a false declaration, the claimant must deny a fundamental aspect of the claimant's identity."
It was akin to requiring a person of Asian ethnicity to "declare their ethnicity to be either 'white' or 'black', or requiring a bisexual person to declare their sexual orientation to be either 'heterosexual' or 'homosexual'."
The judge is being asked to quash the policy and order that it be "reconsidered according to the law".
James Eadie QC, on behalf of the Home Secretary, will submit that the policy does not "interfere" with rights under the ECHR.
In written submissions, he argues that if the policy constituted an interference with Article 8 - the right to respect for private life - it was "justified" by the need to "maintain an administratively coherent system for the recognition of gender", to maintain security and to combat identity theft and fraud, and "to ensure security at national borders".
Mr Eadie also states: "The defendant does not accept that the issuing of passports with an 'X' marker could be done without regard to the implications of recognising non-binary status across Government.
"The amendment to legislation and to policy would incur a huge administrative burden as well as a significant burden on parliamentary time. There would be associated financial costs."
There would also be "significant administrative and financial costs" to HMPO.
Elan-Cane said in a statement before the hearing: "Legitimate identity is a fundamental human right, but non-gendered people are often treated as though we have no rights.
"The UK's passport application process requires applicants to declare whether they are male or female.
"It is inappropriate and wrong that someone who defines as neither should be forced to make that declaration."