A Unique Taxpayers Reference (UTR) number is the unique number that is given to you as a freelancer when you register with the government for Self Assessment (self-employed). All freelancers need a UTR number in order to pay their tax bill for each financial year.  You can read here how you can get a UTR number. 

Also you can check out our whitepaper with all the information you need. It will tell you what it is, when you need it and how to get it.