Southampton Waters Speed Limits

[Blue Sunray]

This is clearly not a purported law.
It says "ABP Southampton considers that....". If they prosecuted a master of a vessel no doubt they would want to admit the Notice as evidence. It would be for a court to decide guilt or innocence on the facts.
The preamble to the Notice says it is a reminder to proceed at a safe speed in what is a very busy channel.

You are spouting, to use a technical term, spherical objects. Which internet pages did you study law at?

 

[Roger52]

There was no internet when I graduated with a law degree.

 

[Ian h]

QuestionHow would they actually prove that you were doing over 40knots ??
I only have a top speed of 48 knots so prefer to be on the right side going down Southampton Water