Well that's me stuffed again,
I did get to the point where I could press F9 and then select the Centos EFI entry.
The problem only occurred after Windows installed a BIOS update, taking me from F.65 to F.67. One of the first things I did to try to fix the problem was to roll back F.65.
This morning I thought I would re-apply the update and see if it made any difference. Unfortunately it did. Wnce I was on F.67, when I pressed F9 the menu was missing the Centos option, only showing "
OS Boot Manager Fedora (ST1000LM014-1EJ164-SSHD) Boot From EFI File
While collecting the above details, I tried the last option which then gave me the options:
NO VOLUME LABEL <EFI> <centos> shim.efi
At which point Centos then booted.
Anyone got any ideas what I need to do next.
Also, I tried rolling back to F.65 again to see if that would return the Centos option to the F9 menu but it didn't