Unique Taxpayer Reference Numbers (or UTRs) are 10-digit codes that uniquely identify you or your business. UTR number is a highly confidential piece of information.

Any individual with self-employed income, income from rental property, and for the Construction Industry Scheme is obligated to have a UTR number (UTR numbers are necessary for CIS tax refund registration).
After registration, you’ll get a letter containing your Unique Taxpayer Reference ( UTR ) within 10 working days (21 if you’re abroad). You have to file your Self-Assessment on time, by post or online