Further to CM's point about transition LEVEL, it is worth noting that in times of very low pressure the first available FLIGHT LEVEL above the transition ALTITUDE can be surprisingly high.
e.g.: QNH 983 mb. transition ALTITUDE 3000 ft
Difference between 1013 and 983 = 30 mb (equivalent to c.900ft.)
Lowest FLIGHT LEVEL at which you will actually be above the altitude of 3000ft is FL 40. (and therefore first usable FL NE bound under the quadrantal rule is FL50)
Conversely, in times of High Pressure you can have a flight level which is numerically LESS than the Transition Altitude
e.g.: QNH 1038mb TA 3000ft
Difference 25mb: c.750 ft
The first available FL which will put you above 3000ft AMSL is FL25.
Whilst I would agree that the quadrantal rule (in UK only) is recommended for IFR flight, it would surely be sensible if you are operating VFR above the TA for you also to fly the correct quadrantal. You are increasing your chances of avoiding other traffic, some of which might be bowling along IFR not really looking out and relying upon the Quadrantal rule to keep him away from other traffic. If you are routing along VFR on the QNH at the equivalent of FL40 but heading NE rather than SW you are asking for a surprise!!
Finally, with reference to the base of CAS: Make sure you are flying on a relevant (i.e. local) QNH and not a regional. The 300 ft or so difference provided by the Regional being a FORECAST LOWEST QNH can be enough to put you up inside CAS without knowing it.