The Company Unique Taxpayer References (UTR) is the primary identifier for the company and should be used whenever HMRC is contacted and when tax returns are filed. When a new limited company is registered, Companies House will inform HMRC of the new company and a UTR (ten-digit number) will be issued. HMRC will then issue a letter to the company's registered address outlining important information about registering the company online for Corporation Tax and filing Company Tax Returns. The letter, which will be sent to the companies registered address, will also contain the company’s ten-digit UTR. The number can also be found on other documents issued by HMRC such as form CT603 ‘Notice to deliver a company Tax Return’, Depending on the type of document issued the reference may be printed next to the headings 'Tax Reference', 'UTR' or 'Official Use'. It is possible to locate a company UTR by making a request online at https://www.tax.service.gov.uk/ask-for-copy-of-your-corporation-tax-utr. HMRC will send the number by post to the company’s registered address as shown at Companies House.