There are a couple statements from the U.K..gov site that are relevant, but still depends on what happens.
Dated Nov 6
“If there is no deal, pet passports issued in the U.K. would not be valid for travel to the EU “(says TO not within, so not clear for us)
“Return to U.K.
Your pet must have one of following documents:
1. Existing EU pet passport (both for U.K. and EU) citizens”
And
“There will be no change to current requirements for pets entering the U.K. from EU after March 29th”
But in a later document dated Dec19
“The documents required to enter EU would be the same as an unlisted or part 2 listed country”
In this case the passport would not work to get into the U.K. and would have other requirements.
So the big question is will Barley’s pet passport remain valid even though issued in U.K after Brexit? We will wait and see
When we take Barley to the vet for rabies shot in February, if we don’t have clear information, we may just get an Italian EU passport and also a test for a blood titre test to cover worst case scenario.
We’ll only be traveling to U.K. once we are heading back to US so more concerned about validity of UK EU pet passport, when we travel by train in Italy and Europe a pet passport is required.