Sorry, it was a bit late when I posted that last and I was a bit tired. Yes I had run loadsce, I was just trying to be a bit brief.
Anyway, I had an epiphany at 0230 this morning (as well as extremely low blood sugar level - thanks diabetes) and it turns out the problem is a faulty sd card. I have seen this sort of problem a few times previously on hard drives: in 38 years you see a lot - sometimes it takes some effort to drag the memory out of archive - and there's nothing like the sugar hit of 6 jellybeans to give the brain a kickstart (with the emphasis on hit and kick).
I always get a bad case of insomnia when I go low so I rebuilt again on a new card this morning and all seems well.
Sorry to bother; Its 0740, the wife just left for work, the dogs have been fed, so I'm going back to bed.