Britain could introduce a third gender category to British passports allowing citizens of indeterminate sex to opt out of standard male and female identification, a Home Office official said on Monday.

Under the proposals, those of indeterminate sex may be able to use an "X" to denote their gender on passports, rather than "M" or "F".

"IPS is considering the gender options available to customers in the British passport, "an Identity and Passport Service IPS.L spokesman said in a statement.

"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. Any changes to the UK passport would need to satisfy our rigorous security requirements," he said.

Current regulations require transgender and intersex people to decide on a gender, which may not necessarily match the one adopted by the passport holder in practice.

Those undergoing gender reassignment operations are only allowed to adjust the gender in their passports after completing the sex change process.

Supporters say changes to the system will help the transgender and intersex community avoid embarrassing situations at passport control if their appearance does not match the gender stated in their passport.

The consultations follow the introduction of an opt out system in Australia last week, which meant citizens need not undergo sex change surgery to alter the gender on their passport, and may now nominate male, female or indeterminate as their sex.