I think that it is on the SRN (Strategic Road Network) from Manor House northwards. This is a different subset of London's street network which effectively permits TfL a veto on schemes there, although they are not the highway authority. South of Manor House, Green Lanes is just a principal borough road.
Green Lanes isn't on the TLRN (Transport for London Road Network):
http://www.tfl.gov.uk/assets/downloads/TFL_Base_Map_Master.pdf
I think that it is on the SRN (Strategic Road Network) from Manor House northwards. This is a different subset of London's street network which effectively permits TfL a veto on schemes there, although they are not the highway authority. South of Manor House, Green Lanes is just a principal borough road.