In message
,
lonelytraveller writes

Ah right, thanks, that seems to fit. Except, why is it above ground?
Wouldn't a signalling station need to a physical connection to the
northern line?

It only needs electrical connections. I don't know quite what they have
in mind, because signalling for each tube line is run from a central
control room - in the case of the Northern, that is currently in Cobourg
Street (from where the Victoria line is also run). Cobourg Street is due
to close once resignalling is complete, at which point the Northern line
control centre moves to Highgate. I don't know what they have in mind
for Kennington - it could just be an unstaffed relay room, or perhaps a
secondary control centre in case of problems at Highgate.
--
Paul Terry