register for self employed online on the HMRC website, then select to register for Self Assessment. The system may require a Government Gateway user ID and password. When you have logged in, follow a path to doing your paperwork to become a sole trader. Some of it would be a description of your business, and other information such as, your personal information. Once you’ve completed this process HMRC will send you a UTR by post. It’s quick to register online and it means that you’re ready to handle your tax responsibilities correctly.