I was on the way to university when this was going on. At Westminster the service update announcement was saying that the Jubilee line had severe delays due to signalling problems. On the train, we waited a bit before departing Westminster and the driver gave an announcement saying there were multiple failed trains on the line and so the journey to Stratford would be slow. Held at London Bridge for about 10 minutes but then all okay to Canary Wharf.
i was at london bridge trying to go westbound at about 8.20. there was a train in the platform with the doors closed but unable to depart. this lasted for around 10 minutes (the doors were not re-opened - lots of confused people staring back to us on the platform through the glass). eventually it did move off, i assume in some kind of restricted manual mode.
another train pulled in and doors opened for people to board and re-closed. this time they tried to depart, but decided it was not possible (or not worth it due to speed of RM?), so they de-trained. the train then sat there all the time I was waiting (i gave up at 8.50 and re-routed). at one point the driver got out to 'isolate the traction current at either end' (i *think* this is what was said - I overhead him talking to the platform member of staff).