"MIG" wrote

And all electrified parts of the current London Overground were four
rail at some point, weren't they? Ah, maybe not Dalston to Stratford.

nor Kensington Olympia - Clapham Junction (though Willesden Junction HL -
Kensington Olympia was 4-rail from around 1914 to 1940). For completeness,
two other stretches of the LO are electrified at 25 kV OHLE, though used by
LO diesel trains - Barking to Woodgrange Park and through South Tottenham
station.

Peter