Hi,

First message here. i actually worked on the upgrade project at marble arch.

i believe this is on the eastbound platform, if you go near the head wall. there is a new metal door before all the (E switch rooms). this leads to the old exit for the station. and now is a disused vent shaft. but in that disused area there is a red door, which you can go through, then down some stairs in to the old pump rooms. and there is a little corridor with a work bench and the door is at the end of it... sorry to say no ghosts lol