Thank you Francisco.
Good to know for future upgrades, if I ever dare attempt another FO upgrade (too many failed attempts and lots of time has been spent already.. thank something for backups is all I can say!)
I suspected it was as you said, however, I did notice in the command line when I first tried to go from 2.2.2 to 2.4 that the system first ran an upgrade to (one of the) 2.3 versions. Though I didn't copy that notice (I should have), it then produced errors going from that 2.3.x to 2.4 - errors I had to go in and correct in MySQL directly..
Again, thanks for providing some help however!
PK