A Unique Taxpayer Reference (UTR) is a ten-digit number assigned by HM Revenue and Customs (HMRC) to individuals and businesses registered for self-assessment in the United Kingdom. The UTR is used to identify taxpayers and is required for a variety of tax-related tasks, such as filing a tax return, claiming tax reliefs, and communicating with HMRC about a tax matter.

Individuals and sole traders are automatically issued a UTR when they register for self-assessment, and partnership firms are issued one for each partner. Companies and Limited Liability Partnerships (LLP) also have UTRs.

A UTR is unique to each individual or entity and cannot be used by anyone else. Once you have been issued with a UTR, it will be used for the duration of your self-assessment registration and will be used for all communications between you and HMRC. It is important to keep your UTR safe and secure, as it can be used by fraudsters to file false tax returns in your name.

If you have lost your UTR or haven't received one, you can contact HMRC to request it again. You will need to provide personal information to verify your identity before they will issue you a new UTR.