Have Defender 110 Pick up. Could do with a rear work light off the back of the Cab. Already have a front light bar with 3 lights on top of cab. But would need rear light switched separately and presumably it's own relay. Or perhaps a low current LED taking a feed from inside light?? Perhaps permanently live with a switch on the light itself? Looking for some inspiration and suggestions please!

Just wire it in on separately. Anything that draws over 20amps (under 20amps you can get away with a carling switch) will need a relay.

Fit a normally closed relay fed from ignition that will go open when ignition turned on cutting power to work light so you can't leave it on while driving, and a manual on off switch in the live feed to the lamp.