Hi,
You can close this thread now.
I was able to upgrade to Windows 10 with the printer unplugged, but then the recent KB5001330 update bug started BSOD'ing the PC, and I was half way through the printer install at the time, which has broken Brother Utilities. It has become a mess.
We've decided to just go for a new PC and printer now and start again.
Thanks for all your help.