According to the Polish authorities, I can take the JAA PPL(A) examinations abroad and these will be accepted by the Polish authorities
Firstly, there are no JAA PPL Theory Examinations, they never produced any!
Each State uses its own National PPL Theoretical Examinations for the issue of a JAA PPL (The same will apply under EASA). Consequently, they are different in every country.
You can take the UK PPL Examinations at any UK Registered Facility or approved FTO that holds them. Simply call a school in a convenient location and make the arrangements.