Thanks again.
I certainly have learned that "oils ain't oils" to coin an advertising phrase.
Yes my laptop will not boot from my bootable SD card but it will boot from the same SD card when 'installed' in a usb reader. I had hoped that creating the bootable SD card selecting UEFI boot mode would allow me to. So the SD card can only be used in the laptop as a storage device.
Oh well I have learned heaps from this thread, thanks to you all, and will now set up a 'pen thumb' usb memory stick which I can leave in the laptop's usb socket. Unfortunately that leaves me with no spare usb ports on the laptop but that shouldn't be a problem.
Oops I have one last question.
Which is better. A bootable usb stick on one partition or a bootable usb sticck which has a fat32 and ext4 partition. Please also advise reasons.
Thanks