Not very accurate. The establishing shots at the start show some South West Trains Class 450 electric multiple units. These are used for commuter and medium distance services from London Waterloo station, which is where the shots were filmed. They run on busy lines with at least two tracks, and are powered by electricity from a third rail alongside the rails that the train wheels run on.
The interior shots in the train seem to be filmed in a studio mock-up 'train', possibly created using CGI.
The outside shots when the train stops (when the scary part starts) are puzzling to anyone who knows UK railways, because the line is unfenced single track, and there is no third conductor rail. Also, the train from which the passengers disembark seems to be either CGI or made by scenery carpenters out of wood.
It is quite common for trains to leave London terminals late at night. The last trains to leave Waterloo are around midnight.
The railways in the UK are pretty high-tech and the drivers are able to instantly call a control room, and report any problems. GPS equipment on trains report their speed and position to controllers in real time. There is a rule that passengers do not leave a train stranded between stations until assistance arrives, in fact passengers who do so may be guilty of the criminal offence of 'trespassing on the railway'.
It is probably worth noting that Britain's railways contain many busy intensively worked lines with fast freight and passenger trains, and the operating people are reluctant to allow film makers to disrupt things. Film and TV show makers have to resort to expedients like CGI, use of library footage, filming on preserved railways and hoping that viewers will not notice, or care about, inaccuracies to do with rolling stock, infrastructure, (e.g. Why are they travelling in a carriage built in 1954 and withdrawn in 1970? What is that locomotive - I thought the service was a multiple unit! Why does a busy main line have only a single track?) etc. In general Joe Public does not know or care about such things.