From compiling all of the information given here (well most...I bought the guitar new...it being a centenary edition of the Gospel..partly because it was a Gibson, mostly because it sounded extremely well with my voice) I'm sensing it is an intonation problem.
It does happen all of the time, probably always has and maybe I'm just developing a keener ear than the one I had when I purchased?
It is exactly when fingering G that I notice it, ie.3 fret. Stu, thanks for pointing out the E tuned to a 440 calibrated A, for a brief moment in time I was feeling a bit like an eejit. B,dubya, I've been working with your suggestion of tuning it a bit off to begin with and compensating with the avoidance of ever playing it when it is open. I guess I knew it was an intonation problem but was wondering if it was something I could repair on my own. Luthier sounds like the way to go, there is a very good one here in Dublin.
Thanks everyone.