A campaigner who wants the government to provide gender-neutral passports will have their case heard at the Court of Appeal later.
Christie Elan-Cane wants passports to have an "X" category, which could be used by those who consider themselves neither fully male nor female.
The campaigner believes the UK’s passport process is "inherently discriminatory".
They lost a High Court challenge over the issue last year.
The issue will now be heard by judges at the Court of Appeal on Tuesday.
Currently, all UK passport holders have to specify whether they are male or female. First Dutch gender-neutral passport issued
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Christie Elan-Cane, who has fought to achieve legal and social recognition for non-gendered identity for more than 25 years, says this is "unacceptable".
Speaking ahead of Tuesday’s legal action, they 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." During last year’s High Court proceedings, Christie Elan-Cane’s lawyers challenged the lawfulness of the policy administered by Her Majesty’s Passport Office (HMPO), which is part of the Home Office, arguing that it breaches human rights laws.
Ruling on the case in June, a judge said that although he was not at that time satisfied the policy was unlawful, part of the reasoning for the decision was that a comprehensive review had not been completed. ‘Important questions’
In the High Court hearing in April, Christie Elan-Cane’s lawyer, Kate Gallafent, claimed the policy breaches two articles of the European Convention on Human Rights: the right to respect for private life; and the right not to be discriminated against on the basis of gender or sex.
But the Home Office made submissions to the court that the case should be dismissed.
James Eadie, acting for the home secretary, said the policy maintains an "administratively coherent system for the recognition of gender" and ensures security at national borders.
Anne Collins, of law firm Clifford Chance said: "This case raises important questions regarding the right to respect for individuals’ gender identity for those who do not identify exclusively as male or female, including members of the trans community, intersex people and those who identify as non-gendered.
"X passports are crucial to the protection of the human rights of this group of individuals."