Limited Vertical Airspace
Going back to the limited levels scenario....
The ANO states IFR requires 500 ft separation based on the quadrantal rules (QR) whilst MATS Pt1 normally requires 1000 ft vertical separation for IFR separations (500 ft may be used in an emergency). Perhaps, the use of emergency separations are about to become more usual (or more akin to the ANO) for the 'reasonable controller'. So how how would the aviation lawyers play that one?