As a Guard at Bath Rd, I was on the 07.30 HST to Birmingham, when doing 110 mph the Driver gave a full brake application, I saw nothing, but he spotted a red flag 3/4 of a mile away, and we ran through 3 dets, it was a broken rail.
The Driver’s master key needs to be in before the engine can be started. So whilst not an ignition key, a key is needed, as you can see at three minutes in.