Bingo!
I was using the recommended Jeelib v12 on my GLCD sketches. Using JeeLib from 10th Sep 2015 GitHub - jeelabs/jeelib at f097c0039c926881d80a74bec7a7aa020de610ee in my Arduino library instead has fixed it and the display has come to life!
Happy Bunny - now to send proper data rather than dummy data! 