Anjouan,
I'm not sure there is as much confusion as you have indicated - we live in an era of harmonised regulations and the certification basis for all western aircraft (and now probably the Eastern European) is FAR/JAR.
As far as CAA regulations are concerned, they are a feature of the past as EASA (using FAR/JAR 27/29) is now the certificating authority for Europe.
Even ICAO Annex 8 is in the process of being amended to recognise that fact.
Jim