OK, cardinal sin is that I forgot to run screen, in my excitement.
Anyway, it hung up and when I tried to choose an option in Clonezilla, the arrow keys gave me these characters typed in the terminal:
Now I have no access via the web GUI, I just get a 403 Forbidden nginx error. With no web GUI, I can't tell the system to single boot from Clonezilla, so I can't restore. I still have SSH access via the CL, so is there any way that you know of that I can ask it it to reboot to Clonezilla?
Interestingly, i did notice this when I was upgrading:
resolvconf.postrm: Reboot recommended
Errors were encountered while processing:
This came just after this (I think):
apt-get install usrmerge
So defo some problem there.