The decisive factor will be the date on which the transport of the goods commenced. In concrete terms, this means that if the transport was started before 31/12/2020, the goods retain (non-Union) status if they arrive after 01/01/2021.
For example: a German window and door manufacturer has a truck depart to the UK on 27/12/2020. Due to delays en route, the truck cannot take the ferry to the UK until 03/01/2021. The goods will be treated as Union goods in the UK, provided the Union status can be proven (e.g. with a T2L).
However, new rules will apply for transports that start after 01/01/2021.
For this, we refer to Article 147(1) of the "UK withdrawal agreement".
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