by Graham Moir.
Ken, thanks for taking the time to reply in such a detailed way. Yes, this is a shared hosting environment, and yes I'm restoring backup created on that server to the same server - but different instances of Moodle.
I haven't taken the route of increasing timeout limits etc. because your other suggestion regarding the file repository gave me the workaround I needed. I downloaded the backup and manually FTPed it to the other Moodle repository folder and then restored from there without problems.
I take your point about just looking for the backup file and avoiding download/upload, but all is sorted now.
thanks !