Tim Roll-Pickering wrote:
Just noticed on Wikipedia that originally it was hoped to take the Northern
Line beyond Morden and onto what's now the Thameslink loop to run down to
Sutton - see http://en.wikipedia.org/wiki/Morden_...ailway_station

How far apart are the lines now and what would, other than line capacity,
carriage size and cost, would prevent such a connection being made today?

By strange coincidence, clearing out my inbox this evening I find a
link to an article on the planned construction of the Wimbledon -
Sutton line (by the District Railway) with the idea of through running
from the extended Northern Line to Sutton. The Southern Railway were
against it and the result is what we have today.

See http://www.semg.org.uk/RlyMag/WimbledonSuttonRly.pdf

regards
HN28