Centaurus,
It was never an "ICAO directive", it was Australia conforming to ICAO SARPs (PANS/RAC 4444 and Annex X, Vol.II, from memory) at long bleeding last, after a string of serious incidents cause by Australian unique "radio procedures". It was over much resistance from a number of Australian domestic pedant pilots, to whom bar room barrister strict grammatical construction was more important than effective and clear minimum risk (aka safe) aeronautical communications.
Left (and right) had always been directions of turn, both militarily, and in civil use elsewhere but Australia. As you probably remember, turn instructions, up to that time, were not read back, again introducing ICAO conforming read-back rules also encountered great resistance in Australia.
Seeing that I was well acquainted with the authors of the submissions on the subject for BAR, AATA, Qantas separately, Ansett likewise, AIPA, AOPA and RFACA, who all agreed, I can remember it all too well. AFAP was thoroughly outvoted.
Chris Scott and peekay4 are pretty much on the money.