SixDelta, sorry if I ruffled your feathers. I don't think you'll find a definitive answer, even SRG will give you an interpretation (although it may be true thay have the power to enforce their will) but that will only apply to UK Civil airports (i.e. the minority of airfields)
Listen to the clearance. Like I've said before ATCOs have to think carefully about the wording to avoid ambiguity (and therefore most of the time will get it right)... pilots have to listen carefully to the clearance and fly it as given. If in doubt ask... approaching feather ruffling stage once again!!!!