Hello!
...above you a pilot could be in CAS without a clearance - if they are caught, chances are nothing more than a written warning from the CAA.
I wouldn't be so sure about that. Just look here:
http://www.pprune.org/private-flying...l-summary.html
Greetings, Max
NB: Wouldn't it be a smart idea to hold aerobatics displays and competitions in controlled airspace in the first place? Like inside control zones of airports that don't get much traffic on weekends. It works nicely in my part of the world!