So as not to be vague, and since I just pushed a version I'm starting to be vaguely happy with...
https://tylereaves.github.io/uk-rail-map/
This is the result of probably a few hundred round trips. The really interesting part of the problem is keeping it both relatively true to real geometry, while greatly exaggerating it horizontally so you can actually see the individual running lines/sidings, like a signaling schematic.
Fascinating. Can you explain why southern London is DC while northern London is AC?
I love computational mapping projects, because there is this hard problem of which towns to show on the map.
Your Scotland map shows towns without rail (although some had rail previously, like Callander, Aberfeldy), it prefers insignificant (population-wise) places while ignoring the larger cities next to it (Scone instead of Perth, Bannockburn instead of Stirling, Inverness is missing, Dundee is missing, Aberdeen is missing). All these places are drawn on the map, but not labelled.
All this clearly shows to me how bad it is. Yes it makes it look pretty, but given your task, I would have expected to give you meaningful map labelling.
Something basic like this would get you a long way:
Having said that, its pretty cool to see the new and old network when zoomed in (assuming that it is half-way correct)