by Ed Snowdon (no, not THAT one).
Emma,
Doesn't the command below do that?
# chmod -R +a "www-data allow read,delete,write,append,file_inherit,directory_inherit" /path/to/moodle
This was the only command in the Moodle install documentation that I did not execute as I was uncertain as to whether it was actually required. In any event, I later tried that command as suggested in the Moodle documentation and it failed, complaining about the +a portion of it.