If you’ve been earning any income at all off of self-employed work you must register for a self-assessment and Class 2 National Insurance. You must do this even if you have completed tax returns previously.
If you do not register by the 5th October of your business’s second year you are at risk of being fined.
If you have sent a tax return before you and register online (form CWF1). You will need to know your UTR number that was used when you registered for a Self Assessment previously.
If you haven’t previously sent a return before you can register online and get your UTR number as well as be enrolled for Self Assessment.