In the worst case scenario , UK as an unlisted country, you would have to wait 3 months after the blood test is successfully completed. That's why they say the process overall takes 4 months. I can see plenty of spare pet cabins in the run up to Easter!
If Great Britain becomes an unlisted country
A current EU pet passport issued in the UK will not be valid for travel to the EU from 1 January 2021.
Before your dog, cat or ferret can travel to the EU for the first time after 1 January 2021, you’ll need to take the following steps.
You must have your dog, cat