This is your company’s unique taxpayer reference. You need this number to be able to register for business taxes like Corporation Tax.
A UTR will be issued by HMRC and posted to your registered office address a week or two after incorporation - you don’t need to contact HMRC to get this number, they will automatically issue one when Companies House notifies them about your company incorporation.
UTRs are 10 digits long and printed under a heading like ‘Official Use’ or ‘Reference’ on any official letter you get from HMRC. Click here to view an example letter and UTR.