All this talk about permissive working ignores a few facts which ruled that out as an option.
For the first half hour or so all trains were stuck with power on, with the possible exception of the one trying to exit Lewisham and head to Blackheath, which was stuck because it couldn’t draw power. Whether it had enough power for heating, lighting and PA is not clear.
NR arrived on scene and switched off the power for that line only to enable them to clear the ice from the conductor rail. At this point the train behind would not have been able to move forward to assist. The expectation was that within 20 minutes the ice would be clear and all trains would be on the move again.
Unfortunately before the hour was up, someone detained themselves. It is not clear which train this was, but once there was a passenger loose on the tracks, the power had to be cut to all lines through Lewisham.
This caused the delay to be extended, whilst the train in question was resecured and the passenger confirmed to be safe. It also meant the passengers remaining in that train were now getting very cold as the doors were open and heating off.
This extended delay led to more passengers detraining, further extending the delay.
SE Twitter were getting quite desperate, pleading with passengers to stay on trains. Each tine they were ready to resume power, someone else jumped off, resetting the situation. This spread to more trains in the queue, causing the area affected to extend, leaving more trains in the dark.
The total delay would probably have been up to an hour had it not been passengers detraining. Instead the trains at the back of the queue were heading towards a four hour delay by the time everything was moving again.
I imagine it was a really tricky situation to manage. They were probably 20minutes away from getting everyone moving for about three hours.