In message , Nick
Cooper 625 writes

Flood-door dating from WW2. These were fitted at various stations
where a bomb breaching adjacent water mains might endager the running
tunnels, or where one line flooded due to a bomb breaching a tunnel
under the Thames could flood into another line. These are still
visible at a lot of stations, such as at the foot of both escalators
linking the Northern Line with the National Rail (formerly Northern
City Line) platforms at Moorgate. They could also be seen in the
end-of-platform tunnels between the Piccadilly and Northern Lines at
Leicester Square, but they were faced and tiled over during
refurbishment work late last year, although the it's still fairly
obvious where they are. If you look at the northern ends of both
Northern & both Bakerloo platforms tunnels at Waterloo, you can also
see the remains of the track-side flood-doors that would have been
closed had any of the under-Thames tunnels been breached.

At Bethnal Green too; I've taken pictures of the winding mechanism.
--
Kat Me, Ambivalent? Well, yes and no.