The fourth rail was retained and bonded to one of the running rails to assist with traction current returns.
I note that the 1937 cable run is still in place, as are the 1904 ceiling tiles. I've not been on the line in a while, but if you were to take an LT scale plan for the line you could still see where all the blockjoints were - BR just removed them and welded the rails together.
Photos from NR's KGX Twitter showing the new tiles in place at Essex Road aswell as some of the tunnel cleaning work being done. Hilariously, the stations have still kept their frankenstein appearance even with some fresh tiles!
I believe the technical term for this is "a bodge".
It's amazing how the walls are now on their third set of tiles in the last 44 years, yet the original ones on the walls lasted 72 years and are still on the ceilings without any issues.
Yes, I would often think when watching sheets of tiles falling off the Victoria line, why doesn't this ever happen to its Edwardian predecessors?
Tiles on the Victoria line were installed using an unusual method. They were soaked in water and then fixed to wet render on the wall.
Everything was fine as long as they interlocked together.
Dislodging one loose tile could result in a lot of tiles falling off.
There are still some stations on the Northern line (and St James's Park) where there are vitreous enamel tiles with flanged edges which were fixed in the same way. The flanges dug into the render. It worked.