Some countries enjoy a reduced preferential rate of duty with the UK.  The reduction is allowed either because they are not fully developed commercially compared say to the USA, which does not raise origin preference documents for European imports.  Sometimes the reduction may be because the country’s government has committed to reducing arms or drug trading, which can be verified by the UK, and so they too may benefit from a reduced trading agreement.

These documents are usually either EUR documents or GSP documents (there is no hard and fast rule which country will issue which type of document, but your agent should be able to inform you which preferential group your sellers’ country belongs to).

As of July 2018 for example Trinidad and Tobago are part of the ACP group (African, Caribbean & Pacific) which can issue EUR forms, whilst Vietnam is part of the Generalised System of Preferences group that can issue GSP forms.

These forms can either reduce or negate the import duty paid on import to the UK.  If you do not produce this document on import, you can if you want, pay the duty on deposit, and reclaim the import duty on later submission of the preference form.  Some countries like Turkey have their own preference form, an ATR1.

These documents do not provide a blanket reduction of duty for all products, and may reduce duty on one commodity code, negate it on another, and not be applicable to the third.

In some cases the supplier overseas may be authorised to ‘self-authenticate’ their commercial invoices, to also act as a preferential document.  For those that can do this, they will have an approval number that the UK will recognise, and validate on inspection of their commercial sales invoice.