There are many legal aspects to consider including name change and legal documents:
The Gender Recognition Act 2004 created a process to enable transgender people to get their UK birth certificates and legal gender changed. The transgender person can apply to the Government’s Gender Recognition Panel for a Gender Recognition Certificate. If they are successful in their application, the law will recognise them as having all the rights appropriate to a person of their acquired gender.
Most transgender people change their first name to something more gender identity-appropriate for them, this can be done via Deed Poll. Your Named Professional can advise you on this. They also may want others to address them in a different way (man, woman, non-binary) and to have the sex indicated on personal documents and records changed.
The policy of the Passport Agency has always been to facilitate issue of a replacement passport when the applicant has changed their name and social gender role, backed by a letter from a medical professional to confirm that the change is for gender reassignment and intended to be permanent.
Criminal Records Bureau (CRB) checks are now called Disclosure and Barring Service (DBS) checks. You can contact the DBS sensitive applications team if you’re a transgender applicant and you don’t want to reveal details of your previous identity to a potential employer.