I was forced to create a new test site from scratch after a dodgy configuration setting caused my old one to crash and I was unable to restore the backup. Even deleting the subdomain and all its associated files didn’t help — something was lingering around somewhere in WordPress’s structure of 5000+ files which was sabotaging my attempts to recover the contents of the backup.
Tomorrow I’m going to find out how to restore a backup into a different subdomain and subdirectory to the one it was backed up from. If anyone out there knows how to do this — and also knows a bit about https: (I already have the SSL certificates) — please let me know. Or better still, rush round to my house and guide me through the process. I have dozens of hours invested in my old test site and I’m reluctant to abandon it without a struggle.