At this point I see nothing else I can do so I will have to put it down to some controller issue on the board or perhaps faulty BIOS.
Except for one last thing...and it appears to be working
So the solution appears to be that it must use an identical SSD to the original, and the only bootable media I can get to detect it, is a USB built using the HP cloud recovery software.
It is pretty frustrating that it must be done that one specific way, but at least it now works! Now just to remove all the HP bloatware, Mcfee etc.