A small point, but I believe the quadrantal rule is mandatory for IFR flight above 3000' in UK uncontrolled airspace. I was certainly taught that it was during the IR. This then presents a difficulty in large parts of the midlands (where the base of the class A airspace is FL45) when the qnh is low and FL3.0 (and sometimes FL3.5) aren't available. Also, FL3.0 can be below your MSA.