Sex-free British passports could be brought in to allow transgender people to opt out of identifying themselves as either male or female under plans being considered by the Home Office.
Under the proposals, the UK passport could have a single box marked "sex", which could be marked with an X.
The consultation follows the introduction of a similar system in Australia last week.
But concerns have been raised over the security implications and extra work created for the UK Border Agency.
An Identity and Passport Service (IPS) spokeswoman said: "IPS is considering the gender options available to customers in the British passport.
"We are exploring with international partners and relevant stakeholders the security implications of gender not being displayed in the passport.
"This is at the early discussion stage and no decisions have been taken."
She added: "Any changes to the UK passport would need to satisfy our rigorous security requirements."