Hi,
I did my UK ATPLs in the UK and did my CPL and ME/IR in Greece.
There is quite a long procedure involving your PPL getting transferred over to the state of licence, as you can not hold more than 1 JAR licence at a time.
The New "State of Licence" will then apply to your old CAA, UK, to confim details and then issue your CPL. You then have to fill out a UK CAA from SRG1136 and send off your licence/s.
Im still waitnng for mine to be sent from Greece, and it could take a while- so ive been told.
Dont know any other countries, but Greece definetley accept the UK ATPLs.