Thank you MacManX
It turned out to be a plugin causing the problem.
I renamed the plugins folder via FTP which allowed me access to the admin panel, and deactivated all the plugins. I activated them in turn, and it would appear WOOCOMMERCE was the culprit. I updated it and sure enough…all back to normal.
It’s such a minefield when you don’t know wordpress enough to have the first clue.
Thisis such a great resource. Thank you again!