Harlesden
Member
Clapham Junction-Willesden Junction-Camden Road-Highbury & Islington-Dalston Junction-Whitechapel-Surrey Quays-Peckham Rye-Wandsworth Road-Clapham Junction
It would need to break at Clapham Junction I think, because (and I'm not entirely sure of this) there won't be a platform that's connected to both the WLL and the Inner SLL.
It would also need to use dual voltage units as the NLL/WLL is overhead wires while the ELL/SLL is third rail.