Mystery Walkway

The stairs could be passing over running tunnels or platforms for that station.

A straight tunnel is easier and cheaper to construct. Nobody would construct something like this without good reason.
The design suggests that we are rising to pass over something and descending to pass beneath something else. This would suggest two tunnels beneath and two above, both sets going in roughly the same direction (if they were at a ninety degree angle, the rise and descent would not be possible).
This appears to be a passage at a station served by at least two lines. However, we do not know the distances involved between the stairs and can therefore only get a rough idea of the direction of the lines in relation to each other.
From the fact that the designers have been forced to take these measures to construct the tunnel and avoid close packed obstacles, it would appear that this is a central area station. It would also seem likely that we are talking exclusively tube as opposed to a mix of tube and sub-surface, as this layout would require the tube lines to be at a very shallow depth if passing beneath the Met or District. It does not however rule out the presence of a sub-surface line at this station, which may have been responsible for the tube tunnels being compacted together.
Could anyone add any further observations?

I seem to remember that Regents Park and Waterloo (Bakerloo) had subways like that as, I think the two platforms were on different levels.