I ran a partial upgrade as suggested by update manager (stupid I know, lapse of thinking as you guys had said 'Do not upgrade') and now I have no bios boot menu entry for USB device.
Any ideas folks?
I corrected it the long way round (using Windows as no option from Dell to supply Linux bios file). I had to temorarily install Windows (ohhhh, bother...) and run the BIOS flash file from there and then I reinstalled Linux. I was not happy with the way I had partitioned the drive so I rebooted to start again only to find that the BIOS boot menu entry for USB had gone again.
Heavens above... what is going on?
I have no idea other than there must be a bios upgrade somewhere in the Ubuntu upgrades that is doing this - yes?
Any help appreciated as always. Thanks.