Had this discussion with a trainee of mine the other day, as he was saying "descend altitude 9,000 feet, QNH 998" (we don't say millibars or hectopascals, as we think the pilot reading back Q N H would be enough to make it clear what we mean). After a little research, we found that the concensus internationally (not the UK) was either say "altitude 9,000", or "9,000 feet", but no need to say both. Either altitude before the number or feet after surely is enough to remove any confusion as to what you are saying. And if not, what is listening out to a readback for. If the pilot gets it wrong 1 time out of 1000 due to confusion, you pick it up on the readback and correct him, rather than adding extra words unneccessarily for the other 999 times.
And I agree with Dirty Pierre from OZ, I was trained there as well, and it seems like over kill to say "turn left heading 320 degrees". If the "turn left" isn't enough to twig the pilot that it is a turn rather than a change of level, then the use of the word "heading" should be, and then again as I said if there is somehow still confusion, then that is why you listen to your readbacks.
In addition I never say "descend to altitude 9,000 QNH 998". Why throw a word in there that is also a number to confuse things, when as far as I can see it helps in no way.