You can see here too that Boris/TFLl wants to take control of the routes between Liverpool St and Enfield Town and incorporate them into the Overground system. This would be great because the North of Tottenham would then have a metro-type system, immediately boosting its attractivity for urban commuters and wouldn't have to rely on SPURS for its livelihood!!
I wonder why Haringey isn't promoting this? The lines exist already and it is easier to achieve sooner than the really heavy investmet required for Crossrail 2 which is necessary too.
Page 25 of this pdf doc
Nice document by Boris .. no wonder he wants to partition off London from the rest of the UK! Those charts make very good viewing ..