South West Trains services to and from London Waterloo were hit at the height of the evening rush hour, on one of the hottest days of the year. The disruption was caused by 'heat related' engineering work outside Waterloo, and signalling problems near Haslemere in Surrey.
South West Trains said: "We would like to apologise for the disruption our customers will face on their journeys home tonight. As a result of emergency engineering work to fix a track defect, we are unable to use four platforms at Waterloo which is having a serious impact on services."
Commuters have been venting their fury on Twitter, and posting pictures.
More top news
The High Court has agreed to a Sussex Police request for access to footage of the Shoreham air crash, but has rejected two other requests.
Wednesday's weather for the east of the region
Wednesday's weather for the west of the region