Just think of all the completely un-necessary 'air conditioning' services they offer!
From this statement I'll conclude that since it never stops pi$$ing with rain, or gets above 20c in the Scotland that i can leave my A/c service until next year!
Thats c£40-50 more for mods next month 
Just leave it - seriously. If your air con is working - it does NOT need servicing. It is NOT part of the official service schedule, therefore isn't a requirement for maintaining warranty.
I thought the oil in the a/c system was hygroscopic and it was prudent to have it changed out every couple of years?
The PAG oil simply mixes with the refrigerant fluid - weather that is 'water-based' - I don't know. But as AudiA8Quattro correctly stated, your air con circuit should be 100% sealed. If they are leaking, or if the compressor has seized, or any other 'mechanical' damage - those are the ONLY times the air con system should need 'servicing'. But if it working fine, then just leave it alone.
Afterall, do you re-gas your fridge or freezer in your kitchen every two years?
