Thanks chaps, I've seen Hepco and Beckers offering but I couldn't bring myself to give them £180 for the privilege of throwing away my existing, perfectly servicable, pannier racks in order to fit a slightly less tidy set... (damned expensive tail-rack at virtually £200 including carriage

)
I believe it is possible to get an aftermarket rack allegedly for the Skorpion but the one I've seen wasn't a great fit and marked the tailpiece

(I'm glad to say not on my bike!)
The rails of the existing pannier mounts are about 31cm apart though, and a colleague at work tells me has a generic black rack and large givi topbox sitting in his shed, so I reckon the money I would save getting that, over
anything new, should more than cover the fabrication and welding of a couple of mounting tabs each side to bolt it to

Of course if the width turns out to be wildly different I may have to reconsider, but he reckons it will be pretty close and he's a mechanic to trade(!) time will tell.....!