I've finished re-watching this series for the fifth or sixth time, and something's just leapt out at me. I don't know whether this was intentional on Boris Starling's part, but it finally occurred to me that D.S. Clifton's first name is Jez. Jez...a possible allusion to "Jesus"?
Me too, I can hardly remember licence plates on a good day, let alone a rainy one when i've just been run over by the car in question. Best we just overlook this or the whole concept goes out the window and it was a great series.
I was certain that Jez is some sort of a short for Jesus (so, possibly a name that the character adopted and not its given name).
As for remembering Red, well, the man did step out of the car into the rain, so it is possible that having regained a bit of consciousness, kiddie-Jez simply saw him and remembered the face of the man who he thought must have killed him. Considering the trauma of all this (and its very deep effect), it's not strange that one glance at a face would be remembered for years.
In the film it isn't specified whether or not Jez planned to be a policeman and then to kill the 10 men and Red. So he could of got a job as a policeman later to see Red, and to slowly be driven mad from there on.
For me another clue was right there at the beginning. When Kate and Red are driving away from the scene of the first murder and we see Jez suddenly overtake their car from behind leading to Kate screaming 'Lunatic!' at him. That portends to the craziness of the killer, in my opinion.
My first clue was the choking scene when he saved him. Then he said "Don't ever do that again", I just knew he was the one and needed his death to be according to plan.