Although much of it originated as part of the North London Railway, the current route is the result of a series of amalgamations, closures and reopenings, and has a mix of third-rail and overhead electrical power supply.
Selvom store dele af den oprindede som en del af North London Railway, er den nuværende rute resultatet af en række sammenlægninger, lukninger og genåbninger, og har en blanding af tredjeskinne- og køreledningsstrømforsyning.