Been struggling with it all morning with no success, then as soon as I post here I find a reference on the net that seems to have had some effect. Firstly, I am totally incorrect in assuming the SCSI controller was my SATA HDD, it isn't. My HDD is being controlled by Nvidia SATA controller.
I found some advice on a similar issue being caused by remnants of Daemon Tools Lite, which I had trialled some time ago, and later uninstalled. The advice was to check for a specific driver left by Daemon, in Sys32, which was indeed there. Once the driver was removed, I disabled and uninstalled the iffy SCSI controller and rebooted. Reboot was much improved and iffy controller is no longer there.
Hopefully resolved and waste of a long ramble. ;o) I'll leave unresolved for a while pending further trials.