The driver of the Basingstoke train was off his train and standing by the line-side telephone when his train was pushed forward several feet by the collision. He picked up the receiver and spoke to the signalman, informing him of the collision and asking him to call the emergency services. The signalman immediately switched all the signals he could to 'danger', and signalled to the adjacent signal boxes he had an obstruction on the line. However he had no control over automatic signals, and was not able to stop the fourth train. He then called the Clapham Junction station manager and asked him to call the emergency services. The accident had tripped the high-voltage feed to the traction current. The operator in the nearby Raynes Park electrical control room suspected there had been a derailment and re-configured the supply so that the nearby Wimbledon line trains could still run.