The courts also play a big part in this.
A lower court isnt able to decide on a common law argument put forward as a defence, it would need to be moved up or refered to a higher court. They primarily deal with statute law and statutory obligations. Did you break one of these obligations? then this is where you are dealt with.
You also have judicial review and judicial merit.
If you wanted to argue that council tax is unlawful and is not applicable to yourself, you will be invited to a magistrates court. They cant adjudicate this matter on a common law principal (they may try) but if you know how the system works you would appeal. The case gets moved up a notch, each time a decision is made you could appeal to a higher court, eventually ending up at the supreme court and from there the house of lords.
I suspect you would win your argument, but this is how far they make you take it. In front of the lords of the house you will find that the constitution plays a very important and significant role, that common law is paramount and very much valid.
Most court staff at the lower end have very little understanding of common law and the constitution, if they did they would be working higher up. I wouldnt even enter a magistrates court, its a place of statutory obligations, i live under common law, that means the high court and a jury.
"A ruler who violates the law is illegitimate. He has no right to be obeyed. His commands are mere force and coercion. Rulers who act lawlessly, whose laws are unlawful, are mere criminals".