It would be an interesting, if futile, argument to watch. You were riding about in the dark with flashing blue lights on your bike. That's what the police (and, agreed, other emergency services (although I'm yet to see a fire bike) do). People expect that you are an official because that's what you are pretending to be. You'd be nicked for it and probably end up in court. Much the same as you only need to wave a gun shaped object around to be done for gun crime 'I never said it was a real gun' isn't a valid argument.
Equally, much like TV is the only thing correctly depicted on TV programs, the judicial system gets really upset about people pretending to have their authority. Some might say disproportionately so. So you would be lucky to get a 'don't do it again sonny'.
A spiffing wheeze, and one struck off the bucket list. But I wouldn't let yourself get addicted to it.