It will interesting to see if their action against the Met succeeds.
I'm guessing it won't. Which means that it wasn't a "mistake" but a logical endpoint for the powers the police have.
I am also guessing that a careful reading of the full law would reveal that the police now have the powers to arrest people who are merely watching a protest. After all, the logic would go that people wouldn't be protesting if there was no one there to watch.