Thank you for your post.
From 1 January 2021, plants and plant products from non-EU third countries that enter into free circulation in the EU (having been subject to plant health checks) before travelling on to GB, will be treated as if they were an EU import.
GB will be phasing in import checks for EU plants and plant products from 1 January 2021. More details of the phasing of EU imports can be found here
Plants and plant products from Rest of World (RoW) countries which have had their SPS checks completed by an EU Member State may be accompanied either by a phytosanitary certificate issued by the competent authority in that Member State, or with one issued by the non-EU third country of origin.
If plants and plant products are imported directly or under transit arrangements, such as CTC, from RoW country to GB then those goods will require a PC and pre-notification from 1 January 2021.
Any response to a question is intended to provide only general information about the topic raised and is based on the relevant legislation and wider framework as applicable at the date the response was published. The responses provided on this forum do not amount to legal advice and those asking questions should consult their own lawyers for legal advice as appropriate.