In message . li, Tom
Anderson writes

Horizontally constrained, i can see. Is it vertically constrained? What
prevents the higher floor in the original photo (the link to which has
since been trimmed) being 67 cm lower, so there is no need for steps
down to the lower floor?

The additional steps would then protrude into the cross passage which,
as you say ...

which would in turn mean shuffling the passage a metre or so further
away from street (to the left in the photo).

The passage passes through one of the quite narrow arches of the
original Great Eastern viaduct, so it couldn't be moved left - it would
have to be reduced in width by a metre or so, which I guess would be
unacceptable from the point of traffic flows in the rush hour.

What's at the other end of the passage?

The arrangement is a mirror image of the near end. The rising staircase
at the near end of the passage provides access to platform 1 and the one
at the far end provides access to platforms 2 and 3.
--
Paul Terry