John B wrote:

This leaves the ELL itself. I'm fairly sure this is third-rail from
New Cross / New Cross Gate to Dalston: although I haven't read
anything explicitly stating that this is the case, none of the TfL
publicity pics have OHLE masts in them and I'd be sceptical that the
tunnels have the necessary clearance.
That's what I thought. Brunel probably didn't leave enough room for
future overhead electrification.