A campaigner has lost a High Court challenge calling on the government to provide gender-neutral passports.
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 claimed the UK's passport process was "inherently discriminatory".
High Court judge Mr Justice Jeremy Baker refused to rule the government policy as unlawful.
Currently, all UK passport holders have to specify whether they are male or female.
Speaking after the ruling, Christie Elan-Cane, who has fought on the issue since 1995, said they were "bitterly disappointed" and that non-gendered people are "socially invisible" and being "denied civil rights".
"I was not seeking special treatment. I was seeking to be treated as a human being."
Christie Elan-Cane previously said it is a "basic human right to have your identity".
The campaigner told the Women and Equalities Committee that being non-gendered was "not a lifestyle choice" and "incredibly frustrating".
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.
Male, female and non-binary
The "X" stands for unspecified for people who do not identify as male or female.
Last year, Canada became the latest country to offer citizens gender-neutral travel documents.
Australia, Denmark, Germany, Malta, New Zealand, Pakistan, India and Nepal already have a third category.
The International Civil Aviation Organisation - the UN agency in charge of air travel - also recognises the "X" option.
And, in what could be the first case in the world, in 2017 a Canadian baby was issued a health card without a gender marker.
In his comments, the judge stressed his conclusion was reached on current evidence, adding: "It will be necessary for the government to consider to what extent if any, in an age of increasing social and legal awareness and acceptance of the importance of issues relating to diversity and equality, the recording of an individual's sex and/or gender in official and other documentation is justified."
'Fear to travel abroad'
LGBT charity Stonewall said the decision was "disappointing", saying that "many trans people are afraid to travel abroad for fear of intrusive questioning or difficulties at passport control".
"Non-binary people are also not recognised under law, and it's unclear whether they are protected by anti-discrimination legislation," said Laura Russell, Stonewall's head of policy.
MP Maria Miller, chair of the women and equalities committee, has previously said a person's gender was "not relevant" on passports and driving licences and does not assist with identification.
The High Court ruling comes as the UK government prepares to launch a consultation on the Gender Recognition Act 2004, to consider plans to make the process of changing legal gender easier.
Currently, to change gender people must have lived for two years in their preferred gender and must be diagnosed with gender dysphoria, a condition where a person's biological sex and identity do not match.
They can then apply for a Gender Recognition Certificate.
People can change their gender on documentation including passports and driving licences - but there is no option to identify as non-binary.
Christie Elan-Cane said they cannot comment on whether they will lodge an appeal to the High Court decision.