Thanks Richard much appreciated!
Returned indoors for a cup of tea! I've done the calliper piston polish up, it comes out when you press the brake pedal and you can push it back in. While 2 years ago I think I reported the bleed nipple as 8mm, it is now 7mm and a bit where 7 is too small an 8 is too big. Leaving well alone on that score at the minute so the piston in and out is brake pedal push out, then push back with a wedge of wood, and a flat bolster chisel as a lever.
In decades of diy car fixing I clearly must be missing something in how disc brakes work, and those sliders.
At the moment I cant quite resolve why with the calliper piston fully pushed in as you to to fit the brake pads in position, and the brake pads in place for an easy fit for the positioning of the calliper, why when I place the slider bolts in the appropriate holes....and screw the bolts in do I have a rock solid disc with the pad/pads clamped to the disc, and the calliper piston retracted and not interfering with play.
Must be doing something wrong! Can't quite work out what.
Neil