
I'm not so sure having been onto the DEFRA website (which is a minefield since the UK finally left the EU!!)
I found this -
"Pet travel documents
Your pet must have one of the following documents when entering or returning to GB:
an EU pet passport issued in the EU (or in GB if issued before 1 January 2021), or a pet passport from another Part 1 listed third country
the animal health certificate (AHC) issued in GB used to travel to the EU – which you can use to re-enter GB for up to 4 months after it was issued
a GB pet health certificate (for travel into GB only)
Your pet will not need this documentation if it’s entering GB from:
NI
the Channel Islands
the Isle of Man "
I think you'd best contact DEFRA directly for the situation 'POST LEAVING THE EU'.