The UK doesn’t officially call it a Tin Number Uk , but the term is often used to refer to the Unique Taxpayer Reference (UTR). HMRC uses this number to keep an eye on someone’s or business’s tax responsibilities. Single business owners working across borders, particularly those in the EU, might find that a VAT number has a similar function. Every country has a TIN, in the UK we call it a UTR, and that’s the number an international authority will ask for if you’re asked for a TIN.