It looks like it's sorted itself out. I did have a lockup crash a few
days ago - hence the
top - 23:31:42 up 3 days, 10:07, 15 users,
'up 3 days' bit in top. It was restarted ok, but was that when the
problem started? Hmm.
So I have done a proper shutdown and restart, and it's now back to normal:
Reading package lists... Done
real 0m11.915s
user 0m1.912s
sys 0m0.320s
It will be interesting to see how long this lasts - fsck didn't find
anything wrong with the drives after either restart.
Ian