My main question therefore is therefore, is there any way of recovering the files by transferring to PC and can they be viewed there (XP or 7)?
The only way to recover them is to open the Humax, attach the disk direct to a PC and use humaxrw in recovery mode (-r command line option). The software can be downloaded from Link to humaxrw More detailed instructions can be provided if required. Once downloaded the recordings can be played on a PC.
In addition to what Martin has written, when you attach the drive to the PC do not let the PC ‘initialise the drive’.
If you are using Windows Vista or 7 then open an administrator command prompt (enter cmd in the search box and right-click on cmd.exe then select ‘run as administrator’) then CD to the directory where humaxrw is and enter the command as Martin has described. You shouldn’t need to do this under XP.