That jolly fine chap we were talking with was none other than Neil Price, Mel. Now retired gunsmith but he still writes the technical strip-down and fettling guides for Airgunner Magazine.
That safety spring shown on the Chambers site will be incorrect methinks, John, with Mel's gun having the "single sided" safety. I wonder if Protek may have one? Or, as the chaps were saying, if you could source another little spring (I think the chaps were saying that there was a little recess for the spring to fit in?).