In message , at 14:06:16 on Wed,
13 Dec 2017, Mike Bristow remarked:
What's a plausible alternative?

Problems with substations?

What's the mechanisim that caused it? I'm by no means an expert, but
I can't think of obvious problems with substations that would cause
widespread issues when they're snowed on. Localised issues, yes;
but nothing systemic.

Today there's been a power failure in the Finsbury Park area, causing
a few delays and cancellations.
--
Roland Perry