The HM Revenue and Customs (HMRC) reference number must be linked to an active (live) record and be one of the following.
10 digit individual Unique Taxpayer Reference (UTR).
10 digit Trust and Estate (UTR)
Only enter this if you don't have one of the HMRC reference numbers above.
If you are unsure whether you have an active (live) record you can contact HMRC. For further information about contacting HMRC, follow the links below on GOV.UK