Yes. They have the authority to stop you on the street.
However, you DO NOT have to talk to them. If you were “stopped” in the street by an insurance salesman and did not want to engage them in conversation, you would simply walk away.
Think of it this way – if you have nothing to hide, then you have nothing to prove. If you have something to hide, you do not have to volunteer information that can be used to possibly convict you.