South West Trains has apologised after trains on some of the country's busiest routes were cancelled or delayed yesterday evening because of emergency engineering work and signalling problems.
Services to and from London Waterloo were hit at the height of the evening rush hour.
A spokesman said today:
At 14:00 a two inch kink in the rail was identified outside Waterloo station which meant we had to close four platforms at the station and as such, lost a vital section of track which allows us to run our advertised service.
Train services to and from London Waterloo were heavily delayed for the remainder of the day and many were overcrowded as a result. The decision to run an alternative service plan was not taken lightly and when such a decision is taken we consider the safest and most efficient way of running our network to get everyone home as quickly as possible.
Due to the nature of yesterday's incident and the critical location where it occurred, this unfortunately meant that many customers were heavily delayed on their journey home.
We do everything possible to prevent the kind of disruption you experienced yesterday. I would also like to assure you that we are working hard to replace ageing parts of the rail system to deliver a better, more reliable service.
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The service has 1,366 people rammed into a dozen carriages designed for just 640.