Despite my best efforts I couldn't find the problem but it must have been with permissions in Limesurvey somewhere. The template had been loaded by another person and even with superadmin rights I couldn't save as I noted above. I subsequently copied it (so it saved with me as the owner) resolved it and like you both - no problems. I suspect there was a glitch somewhere because I've had a different site with similar template loads in the last few days and they all seem fine for me to edit.
Coding - one of those things I guess. Thanks both for your help. Lloyd.