Johnson said he picked up the intercom to that door but received no response and thought “Saturday night, someone’s messing around”.
He said while he was speaking to the train manager to ask her to investigate “someone over-spoke us” and he heard someone “screaming ‘there’s a knifeman stabbing people'”.
He thought the “best thing to do was to get to a platform” and the voice of the individual “really drove that home”.
Johnson said he had “probably about 10 seconds” to switch to the slow line, adding: “I just knew that was the right option, it just came instinctively.”
He pressed the urgent button and told a signaller “get me to Huntingdon and get me the police”, stating if he had pressed the emergency one it would have stopped all trains in the area.
The train driver said he adjusted his speed while the signaller had to wait for two minutes in order to switch the points.
Jurors heard Johnson “could hear banging and screaming” on the cab door, and he said: “It was incredibly loud, and people were begging for me to open the door as well.”
Johnson told jurors that if he left his seat “after a short period of time the train will stop”.
“My mind was completely focused on one thing and that was to get the train to Huntingdon,” he said.