You'll only have a UTR if you are registered for Self Assessment. It will have been sent to you by post.
You'll find it on your welcome letter and also on your tax return. It is made up of 10 numbers, for example, 1234567890. Please enter the reference with no spaces.
If you don't complete a tax return
If you get income from outside the UK, you may need to register for Self Assessment and complete a tax return. For more information follow the links below.