Pet owners in Britain will need new documents to enter the European Union with their animals after the Brexit transition period ends on January 1 next year, the government said.
Owners will have to get an animal health certificate from a vet no earlier than 10 days before travel, the government said on its Brexit guidance page.
British pets required only a passport while their country was part of the EU.
Only vets officially allowed to inspect animals for export can issue the certificates.
The same rule will apply for taking animals from England, Scotland and Wales to Northern Ireland.
But the UK government said its approach to enforcing the rule in Northern Ireland would recognise “these changes will take time to adjust to”, without specifying whether there would be a grace period.
Owners will still have to ensure pets are microchipped and have up-to-date rabies vaccinations.
The health certificates will be valid for pets’ onward travel for four months.
There will be no new rules on pets travelling from the EU into Britain, which will continue to recognise EU pet passports.
The EU has given the UK the same status for pet travel as Australia, Russia and the United States.