Observer I note your comments but the reality is that as a general rule, no permits or certificates are needed for keeping or moving a specimen of a species listed in CITES Annex B, C or D inside the EU. See Section 2.2 of the
EU Guidance Presumably someone with greater knowledge than you and I has decided this is legal.

The UK government advises that"You will not be able to freely move or trade species listed in Annex A – D between the UK and the EU."

UK government guidance CITES after Brexit

Furthermore, you will only be able to move protected species through a designated entry point, which does not include Dover and Eurotunnel.

Yes, all this only applies if there is no new deal to cover these issues (a point I made earlier), and surely we must have a deal with the EU at some point. But it is unclear when this will be agreed or what it will say. In the meantime we are about to leave the EU and, unless things change dramatically in the next few weeks, without a deal. The likelihood is that, at least in the short term and possibly for an indeterminate period, these constraints will apply.