Eastbound platform at Lancaster Gate

I think it could be a door.

Sorry, I couldn't resist

I presume you mean "Can anyone reveal what is behind the door?" (to which I don't know the answer).....

Can't find a picture of it, so it's likely I'm wrong, but it might be true.

It could have been the original platform entrance, and that the platform used to be on the other side, but that the side was changed. (1930s tunnel enlargement/modernization would be most likely)

I can: www.flickr.com/photos/crouchingbadger/104382752

I would hazard a guess that it is access to the lift pit (possibly for a cable run?). Power was supplied from Bond Street & Notting Hill Gate substations and the cabling ran through the tunnels. But I never got to check that one out.

There was a few of these doors dotted around the Central Line. Threes one at Liverpool Street on the Eastbound. Which was in my days, was connected by a small wooden bridge, covering the Suicide Pit at that location.

At Lancaster Gate, I seem to recall the lift motor room being above the lift rather than below it. It certainly is since the lifts were replaced in about 1986. I managed to gain some notoriety in being the last person to operate the old lifts at Lancaster Gate. They were due to be decommissioned one Friday night, but on arrival the next day I found both lifts were still operational. So I put one back into service until a chap from the Lift & Escalators department turned up mid morning and turfed me out the lift! They were a nice bunch in those days.

At Lancaster Gate you could certainly access the lift pit from the lower landing adjacent to the lift door. In the pit were a couple of buffers (oil filled possibly) to arrest the lift if it overran the lower landing. Of course if a lift went out of control it would more likely go upwards, as the lift is counterweighted. The counterweights being heavier than the lift and occupants.