Firstly, thank you everyone who tried to help, it was much
appreciated, even if it maybe didn't sound like it (I was getting a
bit frustrated).

As I reported, removing the second disk drive (a 2TB SATA SSD),
allowed me to to the install with no problems at all. I had installed
the drive when the system was running xubuntu 24.04 and it worked
perfectly, I installed a backup of the xubuntu 24.04.

Having got Debian 12 up and running I decided to try and put the 2TB
SATA SSD drive back. It all works fine!

So the presence of the SATA SSD was only preventing the Debian
installer from installing grub/boot, now they're installed the system
boots quite happily with the drive installed.

Very strange! :-)

--
Chris Green

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