@rbmartin

It is true that Wandsworth Road and Clapham High Street are walking distance to the Northern Line at Clapham North, but if you have ever tried to use it in the morning to London Bridge you know that it's already beyond overcrowded.

I think even more people will use the Northern Line when the ELLX2 opens to avoid changing at Peckham Rye for London Bridge.

Also to go to Canary Wharf by using the ELLX2 people would have to change twice (at Surrey Quays and Canada Water), so I suspect a lot of these people will start using the Northern Line as well.