Hi there, thanks again to all of you folks who contributed to this thread.
In the end I did buy and use Blue Grit for half of my moisture resistant wall, and used good old PVA for the other half.
For research purposes.
And in my experience the winner was... PVA!
I can't fault PVA.
Cheaper than Blue Grit, and easier to work on, even on green plasterboard (which I will not use. Ever. Again).
So, for the benefit of future posters on this topic, these are my personal conclusions from my experience:
1. Never use moisture-resistant plasterboard;
2. If it's there, and happens to need to be plastered, PVA it like everything else, and you'll be absolutely fine;
3. Don't waste money or time on Blue Grit, Thistle Bond it or anything else, PVA will do it.
BG ypsum will tell u if skimmed they are no longer moister resistant I still skim the f**k**s anywayI.ve never even pvad moisture boards when I.ve been asked to skim em. Never any come back.. only time I.ll pva a board is if it's been up bout 6 month