Individuals in the Tin Number Uk directly. Instead, HMRC assigns a UTR when someone registers for self-assessment or starts a business. You can register for self-assessment online via the HMRC website or by filling out form SA1. Once registered, HMRC sends the UTR by mail within 10 working days. The UTR is generated automatically when a business registers with Companies House. Keep the UTR safe because it is necessary for tax returns and other HMRC-related activities.