VCP11262 - Unauthorised issue penalty: Calculation and notification of a penalty: Determining the level of penalty
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
Please note: the S 67 VATA 1994 penalty has been replaced by the VAT and Excise Wrongdoing penalty introduced by Schedule 41 Finance Act 2008. The VAT and Excise Wrongdoing penalty applies where a person makes an unauthorised issue of an invoice on or after 01/04/2010. If an unauthorised invoice has been issued before 01/04/2010 the S 67 penalty will continue to apply.
Please see the Compliance Handbook CH90000 Penalties for more information about the VAT and Excise Wrongdoing penalty.
The penalty will equal 15% of the gross amount charged as tax, subject to a minimum penalty of £50, regardless of the number of invoices issued by an unauthorised person.