Success at last!
...or is it for the time being?
Just to fill you in on what's happened in case someone else has a similar problem...
Checkdisk made no progress through phase 4 at all. Eventually, it gave up and told me the checkdisk could not be completed. So I removed the HDD from the system and reconnected with a different USB cable. Viola!
I am in the process if dragging all the new data on there (Stephen Hawking doco, etc) off it just in case! It seems to be behaving itself nicely... time will tell!
Hopefully it's just a suspect cable!
Thanks very much for your help guys! It has helped to keep my language away from the short wavelength end of the spectrum!
Al.