Quoting from the Thameslink website today:
"Earlier today the 07:37 service from Sole Street to London Blackfriars was incorrectly routed into platform 2 at London Blackfriars and blocked the line towards London St Pancras International for approximately 30 minutes. Thameslink services travelling into London Blackfriars were at stand outside and needed to reverse back towards Elephant & Castle to allow this Southeastern train to be correctly placed into platform 4. This is a process that takes time, as drivers need to change ends of the trains and each train has to be reversed through each signal at safety caution, awaiting permission to proceed incrementally.
The train has now been moved into its correct platform and the line has been reopened for our services to run again, however owing to the number of services that run through this area a queue built, and it will take some time for services to return to normal.
Delays caused by disruption leave trains, drivers and crews in the wrong place at the wrong time. This is causing further congestion and delays to services across the network, particularly at St Albans and Luton where trains start and terminate."
In this particular example would the Southeastern driver not have realized he was about to be routed into the wrong platform in enough time to contact the signaler?