Silverstrata
As you say, in the old days, the 'follow the greens' system was visual. But with the advent of milimetric ground radar, I see no technical problem to doing it in fog. Any reason why not?
As good as radar may be, there is too much interference from hangar buildings, passenger terminals, food trucks etc to be highly accurate enough for controlling aircraft taxiing. Despite what you may believe, nothing beats physically looking out the window and seeing the planes when you're controlling their movement around the airfield. It's all very well to see a radar return as a dot on your screen, but that doesn't tell you exactly where the aeroplane's tail or wingtips are.
Been to the tower many times, and seen how it works, but not for a few years due this absurd security issue. Equally, I have not seen a controller on the flight deck for decades, again due to this security issue (last company would not allow it whatsoever). Does your DofT realise they are making aviation LESS safe?
You seem to be familiar with Gatwick judging by your earlier posts. So I presume you fly into there often? If so, like I said before, ask the person in the know with your airline to contact NATS and arrange a tower visit. Although I work in the en-route control centre, I know the tower folks are equally as welcoming for pilots to come visit and see what goes on in the control room. With an appropriate request from the right channel it can be arranged.
I've been on the flight deck many times. Famil flights are still fairly common, although not as much as I would like. I see a number of new trainees coming through that have never seen a cockpit, which makes me wonder how much of an appreciation of the pilot's role and tasks they fully have. I would glady welcome going on more famil flights.