In article ,
MIG wrote:
There was a time when the short escalators were closed, and there was
signposting to a passageway slightly further forward towards the
Piccadilly and on the left, going down stairs.

Yes, it sounds like that is the passage I was thinking of.

This is presumably open most of the time, but everyone would take the
escalator.

I haven't found it to be open on recent visits to London.

-roy