Gender recognition certificate
Stonewall states that a gender recognition certificate (GRC): ‘…enables trans people to be legally recognised in their affirmed gender and to be issued with a new birth certificate. Not all trans people will apply for a GRC and you currently have to be over 18 to apply. You do not need a GRC to change your gender markers at work or to legally change your gender on other documents such as your passport.’
Ref https://www.stonewall.org.uk/help-advice/faqs-and-glossary/glossary-terms