Delays today because, according to journey check:
Earlier today, a train arrived London Waterloo station earlier than scheduled. This caused reduced capacity at Waterloo.
London Waterloo station is operating at its full capacity, especially during morning peak hours. Particularly on busy routes, where trains need to run to a very tight schedule, such incidents can cause knock-on delays that continue for hours afterwards. These knock-on delays often affect both the route with the issue and any connecting routes.
In order to bring the services back to normal, we will be forced to alter some of the services. We expect the service alterations and delays by up to 15 minutes to continue until 12:00
I am a little surprised that a single early arrival disrupts services for half a day, unless this is the Windsor steam train? In which case NR shouldn't be allowing it to run in the peak hours if it's causing this level of disruption.