FOLLOWUP:
I got to the bottom of my problem, and it was simple...
I had mistake on our '3parvasa' user on the arrays, which was configured with only browse rights. Not sure how this happened, as my documentation said edit rights!
I could see "createtpvv: access denied" in the esxi vvold.log files, and oddly I couldnt change authorizations for the user in SSCM, (just a blank dropdown). However re-creating the users on the arrays used for VASA with Edit rights fixed the issue and vvols are back in business!
So point to note for everyone setting up VVOLs, always log on to the storage provider in vSphere with an account which has AT LEAST edit rights on the array/s !
Happy days, even if a pretty dumb oversight on my part.