Issuing a VAT invoice without registration or authorisation can lead to HMRC penalties, even if it is done by mistake.

A penalty may be charged by HMRC when an individual or business issues an unauthorised VAT invoice showing or including VAT without being allowed to do so. The invoice does not need to be a formal VAT invoice; it only needs to show an amount that is shown as VAT or includes an amount attributable to VAT.

An unauthorised person is anyone who is not registered for VAT, not part of a VAT group, or not otherwise authorised to act on behalf of a taxable person, such as an insolvency practitioner or an auctioneer selling goods to recover a debt. Common examples include businesses operating below the VAT registration threshold, individuals who issue VAT invoices after deregistration or businesses who begin charging VAT before being VAT registered. Farmers who are not certified to use the VAT agricultural flat rate scheme, but issue flat rate invoices may also face penalties.

A penalty may be avoided if the person has a reasonable excuse for the error. However, unauthorised issuing of VAT-related invoices is treated seriously and may result in financial penalties.