Another debug launch and target program/erase failure......
final update in case it helps anyone else. I have working (Sort of) on my main pc.
It was this comment from Laurent that gave me the clue:
> There have been in the past some issues on usb with a renesas usb driver to update on some pc.
I realised that every USB port I tried on my PC was USB3.0, all on a AsMedia XHCI 1.0 controller as far as I can tell. Despite updating my driver it still did not work. But changing to a USB2.0 port and it did start working!
I still don’t know what was going wrong, coide and stlink util worked fine on the USB3.0 ports, but at least I have something that allows me to trial system workbench properly.