After some messing and tinkering and going down a tonne (metric of course) of rabbit holes, I managed to get webcam detection working thanks to this lovely stackoverflow page, and now that I see the search terms and the title of the page question I wonder why it took me 3 days to find it????
Anyway, there was some tinkering and a for loop running against Teams processes (in reverse order) as Teams (with its many, many memory hogging instances) didn't want to play nicely with a shortcut key. Thanks Microsoft.
I'm sure there are still bugs in different VC Software, and I can only guarantee this works on 3 versions of Windows 10 on 3 different computers (I wont say which to keep you guessing), but it works for me, and you know what I say about that?