"Tom Anderson" wrote in message
th.li...

Come to think of it, i have no idea how the tunnels relate underground.
Are they completely separate right up their portals?

You'll appreciate this I think Tom, found it this morning:

http://www.youtube.com/watch?v=KZxk08n8Jag

At about 1.03 you can see a connection from Finsbury Park coming in from the
right of the southbound tunnel. That approximates to the current 'up
Moorgate' route from Finsbury Park - the flyover shown above has since been
rebuilt, but that is carrying the down line from Canonbury over the 'tubes'.
The LU tunnel portals were demolished and a new down Moorgate route formed
roughly where they were, passing under the down Canonbury.

I think at the time the film was shot that connection on the right would
have been unused, remains of the abandoned 'Northern Heights' route (which
Colin has since mentioned) that would have extended the Northern Line north
west of Finsbury Park.

Hope that is of interest to you, and many others.

Paul S