The registry would contain the required information
Thanks Bjorn.
My backup regime concentrated on my user data. I must admit I'd not heard of Win10 breaking following a Windows update, but once I started Googling this, I found many examples of other people with similar problems.
Sadly the many options built in to recover from this didn't work for me, with Windows saying it was unable to repair the startup and the Win10 installation image only offering the option to retain my data if I ran it from a working & running copy of Windows 10.
Luckily this makes a copy of some of the folders from the original Win10 installation. It looks like I
may have some of these, but I need to do more digging to work out how to make use of the data as the current Win10 Regedit won't open them