We're really sorry @SW_Help passengers have endured disruption on the Staines line this morning after an overnight problem dragged on into this morning. It all started here, between Staines and Ashford last night (graphic courtesy @traksyuk ) /1

It's a perfect example of how the railway operates as a system, and although it was officially a signalling problem, it really involved all aspects of the railway. The first problem was a track defect caused by electrical arcing (circled). /2

Electric trains take their power from the conductor rail (also called the third or live rail) and then feed it back into the rails their wheels run on, like your model railway. However, of our rails are separated by insulated joints, which is how the signalling system works. /3

The trains' current should be diverted round that insulation using cables and a widget called an "impedance bond". When that widget goes wrong, the current tries to jump the insulation and... this happens. /4

The problem caused our signalling system to "fail safe" and it put this circled signal to red, and stopped trains passing. So while everyone was safe, unfortunately they were also not moving, and we needed to fix the fault. /5

Eagle-eyed people will also have spotted that the stones under the rails look a funny colour, and that brings us to the whole "railway as a system" thing. After a very wet December this part of the track bed was clearly not draining quickly enough. /6

As a result, the track wasn't being supported properly by the ballast (stones) underneath and that also needed to be fixed, along with the impedance bond that started the problem, and the track defect that resulted from all of this. /7

So, we took control of the line overnight when trains weren't running and the plan was to repair all aspects of the issue, to allow trains to run again this morning safely. Unfortunately, we weren't able to get all the work done in time... /8

... for reasons we're investigating now, and we had to come back this morning after 0900 to finish everything and test all the circuits to make sure everything was safe and sound. We're really sorry to people making essential journeys with @SW_Help as this will have caused... /9

... big problems for them. Services have just about got back to normal now and we are absolutely focussed on making sure this doesn't happen again and also finding out why the issue happened in the first place. Please accept our apologies. Thank you.