Thanks Enna. I’ve actually fixed the problem, but still not sure how or why.
I think there must have been some corruption of phpmyadmin, because some weeks ago I’d changed my WP username from the ubiquitous “admin” to something more unique. For some reason, all of a sudden, this new username started playing up by allowing me to login, but then log me out each time I tried to change pages or do an update. As a last report, I tried the old “admin” username, and it worked!
I’ll check out your suggestion though,
Cheers