I see that to use auto-unprotect the box must come alive during the night. I accept that it may be hard work for the system but if, during the day, it is on (not in standby), but not being watched, it would be ideal to be able to decrypt just the file needed - I don't need all decrypted, just the odd one maybe in a month. However, I am grateful for the facilities as they are
You have this wrong.
autounprotect is not the same as
unencrypt.
autounprotect merely sits in the background making HiDef recordings copy and stream just the same as StDef - ie if copied to USB they get decrypted, and if streamed the do not require secure delivery negotiation (so they can be downloaded and ripped). All it does is tweak the properties in the .htm file and the DLNA database.
unencrypt is the one that squirrels away decrypting anything it finds, it needs
autounprotect to be able to do its job (it effectively streams to itself and saves the result as the decrypted file). As installed it only runs between 1 and 6am, but that can be changed, and mine runs 24/7 with no issues.
However, for your requirements, install
autounprotect and create a folder "Decrypt" (or something), use the WebIF to mark it for auto-decrypt, then all you have to do is move any recordings you want decrypted into the Decrypt folder.