TFM, the Moorgate rat hole is the Drayton Park to Moorgate ex Underground line now used by worstrail (formerly the toothpaste line of Notwork Southeast.
I have walked that tunnel on a number of occasions (simulation of emergency/evacuation and terrorist attack). It runs under the Regents Canal... and I can tell you its a wee bit damp down there.
It is also the same station where the very contraversial Moorgate Underground disaster happened in 1975. There are all sorts of urban myths that the train was left in place and concreted in; there is also a lot of disputed regarding the outcome of the inquiry- one numbnut is insistent that it was suicide which, if you read the wikipedia link below it no doubt mentions the driver was rather excited about his daughters fortchoming wedding... hardly suicidal! http://en.wikipedia.org/wiki/Moorgate_tube_crash
Did you know that EDs were also often found on the KX crossrail and down to the Met?
I bet you've never seen an ED running along the Metropolitan. WEll here's a little tip for you- if you look at the throat of KX, on the east is York rd- there is a platform which is now used for stabling the Thunderbirds- formerly the line DOWN to the Met; on the West, just past P11 of the suburban platforms was the line FROM the Met. That's right- trains used to come from afar as Peterborough and run into the CENTRE of London.
Anyway, the point is that EDs came up that way from the South with freight and then went up the line or crossed over onto the North London and over as far as Old Oak to regain the Southern.
Pointless stories, but none the less interesting to those who like these sort of things.
If you click this youtube link theres a whole range of films (the Barbican one is a good one)
http://www.youtube.com/results?search_query=kings+cross+met+widened+lines&aq=f
