All packaging wood (including wooden pallets, crates, crates and dunnage) must comply with the international ISPM15 standard from 1 January 2021. The ISPM15 standard means that the wood has been treated in such a way that any harmful organisms present have been killed. This is a so called HT treatment (Heat treatment). The usage of pallets and packaging can be subject to checks by the health authorities and the frequency of checks is based on a risk analysis.
Please check: https://english.nvwa.nl/topics/brexit
Any further information can be obtained: https://lspalletgroep.nl/heat-treatment/?lang=en