I was on the 17.10 Charing Cross - Ashford (12-car ex-Southern 375) last night which was the first train behind the train stuck behind the one struggling to go up the flyover from Tanners Hill Junction (I think that was a Charing Cross - Gravesend train but will check).
The 17.10 left Charing Cross 14 minutes late and came to a halt at Tanners Hill Junction. The train in front had physically cleared the junction (according to the driver) but was still within the signal overlap. It was reported as going extremely slowly up the hill because of ice on the third rail. At the time we thought this would take a little while, but eventually make it. It was only later we heard that a passenger on that train had pulled the emergency alarm too.
I can't remember when the juice was switched off, but it was when passengers started to detrain from other trains. After around another hour (maybe less) the lights and heating went as the battery power was switched off too. Our train got rather cold. From about 20.45 there was expectation (from tweets and various other messages) that the juice would go back on at 21.00, providing that no more people got off trains and on to tracks. But they continued to do this so it was not until 21.42 that the juice was switched back on. After several attempts the driver managed to get the train to restart (had to build up air pressure, shoes wouldn't go down at first, computer wouldn't reboot etc.) The middle four carriages of the 12-car train would not get power at all, so we proceeded from 21.54 with those in darkness and with no heat. We had just received the green signal a few minutes before, but I have no idea when the train fouling Tanners Hill Junction was removed (though at least by 21.45, as trains were coming past in the other direction by then).
What I haven't mentioned is that morale was actually pretty good on the whole train. People got talking and were supportive and you could see it visibly making a difference, and reducing some people's anxiety. Others only looked at their phones, but it's each to their own. There was only one verging-on-aggressive passenger (in coach 12, I was in coach 1), mostly as a result of drink. No-one attempted to detrain from this train, though that was probably helped by not being within visible sight of a station (we were in the brick retained-wall cutting between New Cross and St Johns, with a tunnel at one end at least).
We got to Tonbridge at 22.58. Exactly 300 minutes late. An additional train was laid on to Hastings.
All in all a trying experience for everyone (staff, passengers, BTP, Network Rail, emergency services etc.). People on or train were frustrated that other trains kept self-evacuating and this was delaying us getting going again. But spirit and camaraderie were good considering the circumstances. Thank you to all who sorted it out (obviously I would like it to have been much quicker, but understand why not).
I am also pretty glad I had the foresight to get some food and drink (shared with other passengers) from M&S at Charing Cross before getting on the train!