Thanks again for everyone's help - really appreciated.
Just to let you all know that by chance I happened to notice a second-hand HP Stream 11" for sale in the local CEX second-hand electronics shop for just £75, so I have bought that. It was a model aimed at school children, I think and has 4Gb ram, 64Gb memory, a good enough screen for reading equipment GUIs and checking emails. It is quite compact, thin, light and portable, even though slightly larger than a tablet. The battery lasted about 8 hours under test, and it can be replaced anyway. Good keyboard.
As it is second-hand and very cheap, with a scratched outer case; I won't worry too much about it being knocked about 'on the road' or nicked. I won't put any personal stuff on it at all, so I can also use it to download files and Apps of slightly dubious security that are sometimes required for my work, but which I don't want on my personal devices.
Good solution
I just need a USB to RJ45 adaptor now - (one with the two LEDs to indicate its connectivity).