Cycle campaigning

For once, Oliver, you explained it more succinctly than me :-)

New York got me thinking. Are there any ex-railway routes in London that could become cycle routes?
Well, there's the Parkland Walk and other remnants of the old rail line to Alexandra Palace (and that doesn't offer such a useful connection), but apart from that, no, I think, but I'm not an expert on that. Certainly, before the East London Line was extended along the Broad Street Viaduct, one idea that came up regularly was to turn this into a cycle route. Disused London rail routes are mostly underground. :)