It's a clear pay up or argue in court up here; it's far easier to go the former unless you have mega evidence against it which I don't think you have.
Code SP30, which is 3 points and £100 fine. It's not going to be more, from my experience if you admit guilt it gets processed quickly at the lowest penalty.
I assume the delay in arrival was the forwarding from the hire company which is outwith the 14 day NOIP regulations, but that is the first thing to double check.
I've had a few! And we don't have the luxury of those
"naughty day courses" instead of the points/fine