We were recently given an instruction that on hearing the request for a zone transit that we were to use without exception the phrase "remain outside CAS". Why ? because so many out there seem to believe once they have requested the zone transit from ATC and are in communication that they may just transit the zone.
Porco Rosso has already explained the lengthy process which can take place at many ATC units prior to a clearance being given.
As for CAT having priority over other flights well yes MATS part 1 again tells us that they do, Dublin Pilot I take it you were filing VFR flight plans not flying airways and thus not going normal routes? if so then you come below normal flights in the priority stakes.
As we say time and time again it is a lot simpler and safer to ask a PA28 to orbit than a B747.
IF you use a unit operating a LARS service they have a dedicated controller juts for you working their socks off trying to give you a good service, if you call up a unit without LARS then there can be a very good chance you will have a very minimum service because of workload issues but you can bet they will do everything they can subject workload to help you out.
WE have limited staffing, LARS is so inadequately funded that it is a wonder any Airport offers a LARS service at all, and so we prioritise. I am sorry if you think you are the poor relation but as with everything in life you get what you pay for, the Airlines pay us, the average PPL does not.