I have no doubt that the appalling revelations about the 'Special Demonstrations Squad' have their origin in the mindset that made use of ACPO as an alternative to democratic policing. ACPO offered Home Secretaries and Chief Constables an easy and unaccountable way in which to do all sort of dodgy and questionable policing that wouldn't stand the scrutiny of democracy in the light of day; the National Public Order Intelligence Unit (which infiltrated environmental groups with agents provacateur) the Confidential Intelligence Unit (which created threats from innocent political activists) and the national Extremism Tactical Co-Ordination Unit (taken away from ACPO by the Met Commissioner from 2011) are all examples of the type of unregulated, uncontrolled semi-detached policing that the 'Special Demonstrations Squad' appears to have been.
The one lesson in this is that the public can never, ever trust the police to govern themselves. At senior officer level they're profoundly corrupt, seduced by power and purblind from ambition. Not one single Chief Constable in the land can be trusted to run his own force without effective public and civilian oversight and governance. Let this lesson never be forgotten.