I've had a go at my wing stay brackets.........
I've binned the half moon pressed metal saddles as i think they are too soft and deform.
I've replaced them with a 6mm thick mild steel plate.
I've used better quality 3/8" diameter exhaust clamp 'u' bolts and locktight
I've used two 'u' bolts on the basis that if one comes losse the other might hang on (per Robin's suggestion). It also means there is significantly more surface area clamped to the upright. The 6mm plate deforms very slightly under full torque on the bolts which I detected as the gap between the wing stay and the wheel rim changes by a few millimetre as you tighten the 'u'bolts.
I've separated the fixing to the wing stays so that any movement here isn't transmitted to the 'u' bolts.
I've used 10mm fixing bolts which gives more head surface area than the 8mm original mounting.
I need to clean up and re-painted everything now...and nowhere near as elegant as Stuart's solution.