Mutt .....You cannot legally detain anyone in this country without police presence ....thats why half the "Police" you see wondering around are really only a visible threat . They are actually normal citizens dressed to look like police and have no power to detain / search etc etc Your CAA bloke is just a citizen so if he tries to detain you , just sue them ....or just shove him out of your way . They rely on people being ignorant of the law and then incriminating themselves .