The scope is a JSR 6-24x50 from Perry190, the mounts are no-name (I don't know it) two piece double clamp high mounts that perry sent with the scope.. by the look of the lovely website, they look like Accushot ones.

CHECK OUT THE WEBSITE.....NEW SCOPES NEW SCOPES

I think I may have spotted the problem, as I put my rifle away this morning.
I have the scope mounted quite far back, and have put the mounts as far apart as possible....this means that the rear mount was on the end piece of the receiver......the one you unscrew at 20 paces distance incase it launches at your head

On close inspection, it looks like I have quite screwed it back on completely.
So the bevel on that piece is slightly out of allignment with the longer bevel on the rest of the rifle.

I shall move the scope clamp forwards tonight and see if this solves the problem.....if not I shall try tuning one round, then the other, then swap them over etc etc etc...anything to avoid shimming!!!

Pete