Can't be sure, but these ODA drawings suggest to me an interchange only
route, - there doesn't seem to be any sort of gateline or entrance for
the southeastern extremity. Perhaps it's emergency escape only? In any
case, the nearest stairs don't seem to be of a large enough size to be
part of a major route


I got a proper look after work tonight (when there was less fear that I'd
have to wait 15 mins for the next tube....) and yes, it has no exit at
the (south) east end, just an emergency exit. I hadn't appreciated that
if you go to the north end of that passageway, then it goes all the way
round below the London Overground platforms. They must have aims for
platform 10a (and 11) as they have new big staircases (which are blocked
off currently....) which would cope with a few extra people.

Is 10a currently used at all....?