You will need to inform HMRC in the Self Assessment registration procedure in order to sign up as self employed. Log into HMRC website with your Government Gateway credentials, select to register as sole trader. Include personal background information as the date on which you began trading and what you do for a living. After you submit, you get your UTR and use that to file your tax returns and pay your National Insurance. An early signup saves you from paying fines and allows you to control your finances well. Visit us: https://accountingbyte.com/how-to-register-as-self-employed/