How to tell HMRC#
GOV.UK's page for a change of personal details is short: you need to tell HM Revenue and Customs if you have changed your name or address, and how you do it depends on your situation. For most people it is one online step. Follow the "tell HMRC your name has changed" link, sign in with your Government Gateway details, or create sign-in details if you have never used HMRC online services, and enter the new name. The same change can be made in the HMRC app.
There is no form to print and, unless HMRC writes to you, nothing to post. GOV.UK says that if HMRC has contacted you asking you to confirm your personal details, its page lists the evidence you can send and how to send it; that is the point at which your deed poll, or a certified copy of it, comes into play.
Your National Insurance number does not change#
A new name does not mean a new number. GOV.UK's National Insurance guidance says your National Insurance number remains the same for life: it exists so that your contributions and tax are recorded against your name only, and it is made up of two letters, six numbers and a final letter. Once HMRC holds your new name, that name sits against the same number. If you need the number itself, it is on your payslip or P60, and you can also find it online or ask for a letter confirming it.
Self Assessment, businesses and agents#
If you submit a Self Assessment tax return, GOV.UK says your details are updated once you have reported the change of name, so there is nothing separate to do for the return. If you run a business, you also need to change your business records, which are held apart from your personal details.
Tax agents, such as accountants, tell HMRC about a change of name or address through their online account, by phone or in writing; the agent route is for the agent's own details, not their clients'.
If you change gender#
GOV.UK's page says your name will be updated automatically if you change gender. The name change and the gender change are reported to HMRC together rather than as two jobs.
Child Benefit is reported separately#
Child Benefit has its own change-of-circumstances page, and it lists a change of name or gender among the changes to report. Only the person claiming Child Benefit can report a change, so if the claim is in your partner's name, they report it. The same page says to tell HMRC if your child changes their name by deed poll. Changing your name with Child Benefit has the detail.
What to have ready#
Your Government Gateway user ID and password, or the details to create them, and your deed poll to hand in case HMRC asks you to confirm your identity. Your employer and pension provider report your pay to HMRC, so tell them your new name as well, or your payslips will keep the old one; that is a payroll job, not an HMRC one.
