Englishal
I was using "tax" in its widest sense.
As far as I am aware the CAA is self funded these days and not subsidised from the public purse. The CAA recovers its costs form the fees it levies on pilots in the UK and aircraft based in the UK. I agree it receives a part of the same fees from maintenance organisations but nothing more. I can see for the reasons I set out above why the EU would want to safeguard its revenue stream without which its ability to oversee aviation would flounder.
For the reasons I gave earlier (and other reasons) it is difficult to see how this could be achieved via indirect taxation (duty on fuel being hypothecated in some way to EASA).
Perhaps one answer would be to levy a "based in" charge on N reg aircraft that are based in the EU equivalent to an EASA registered aircraft and crew. At least EASA would no longer feel the need to protect their revenue stream whcih may be a motivation for their fixation on N reg operators.
(PS I think you will find the fees to keep an aircraft on the G reg a lot more than £75 these days, and of course the fees are a lot fatter when you come to deal with bizjets and the like).