With a bit of good fortune and google I have managed to sort it.
I was uninstalling and reinstalling the drivers when I noticed that in device manager it briefly came up with Viewcon before changing to "USB Audio Device"
Did a google for "viewcon midi" which came up with an entry on the logitech forums where someone had installed logitech camera drivers.
The driver install broke his USB midi install although it still looked OK in device manager.
Just uninstalled my logitech drivers and I now get "USB Audio Device" and "USB Audio Device 2" in REW.
Just need to work out if it matters which one of these I use? I assume one is the input and one the output?
Gary