Business Unique Identifier
This is usually the number issued to you by HMRC, for example your Corporation Tax or Self Assessment unique taxpayer reference. If you don't have one of these, enter your company registration number, VAT registration number or PAYE reference number. If you have been issued with a number from a foreign tax authority, please enter that number here.
If you haven't got a business unique identifier, or any other tax reference number, enter 'none'.