surely all bollocks?
As mentioned before, if the police officer says "Do you understand?" then your response should be "No! I do NOT stand under you in this matter". As before, the question is a Legalese trap and has nothing whatsoever to do with understanding anything which has been said.
Under Common Law, an offence has only been committed if there is a victim (somebody who has been killed or injured, had possessions damaged or stolen or who has been defrauded). So, if the police officer keeps pushing you to agree to pay his company money when you don't need to, then a good question to ask might be "Who is the victim?". An alternative is to ask "What is the charge, or am I free to go?". If you stick to these things, then the police officer has nothing to work on as you have not agreed to be bound by statutes, you have not provided a name and address for him to write on an Invoice (or "Fixed Penalty Notice" as they like to call it) and you have not entered into a "controversy" by arguing with him or into "dishonour" by refusing him point blank.
There is one other thing, and that is, without being aggressive or offensive in any way, you must not do anything which he tells you to do because if you do, then those charming Legalese people can see that as you agreeing to "stand under" him and become subject to his "legal" (not "lawful") authority, and so become liable to those thousands of cunning plans called "statutes", carefully crafted in order to rob you in a perfectly "legal" way.