After the disaster , the latches were redesigned and the locking system significantly upgraded Cause_to_make_progress .

A separate locking system was supposed to ensure this could not happen , but proved to be inadequate .

This therefore Causation disengaged the locking bar on the points for a few seconds before the Scarborough train reached Arriving it , allowing Preventing_or_letting them to be changed Change by the application of the wrong lever .