Servants, not masters.
If after all that you're still surprised that the police would sink so low as to set out to smear the family of a murder victim and infiltrate the groups that were campaigning for his killers to be brought to justice, then frankly, there's not much hope for you. Activists during the 80s tended to assume that there were either police informants or actual undercover police within their groups, such was the reach of Special Branch and MI5, and it doesn't seem to have been much different in the 90s.
Nor have the tactics of the police when criticised or caught acting heavy-handed changed much since then: you only have to remember the leaks to the sadly departed News of the World after the anti-terror raid on the Kalam family, or indeed the stories linking Jean Charles de Menezes to a rape. The Met even went so far as to have its defence barrister in the health and safety prosecution against the force focus on the other smear against him, the fact he had traces of cocaine in his system, as an explanation as to why "he acted the way he did". The fact that he acted perfectly normally prior to his being bundled to the ground and shot 7 times in the head apparently didn't enter into it.
More to the point, these organisations wouldn't have been able to avoid being brought to account for so long if they didn't either have enablers or backers in politics and the press. The bitterest thing about the Hillsborough report was that there was relatively little in it that wasn't already known. It had its impact through having collected all that available evidence, and presented it in such a way that the truth couldn't be denied. As Hugh Muir writes, before the Mail was converted to the cause, it was in the vanguard of belittling those who were calling for justice for Stephen Lawrence. The Met needed little encouragement as it was to attempt to find out what its critics were planning; with newspapers calling them extremists they had just the justification they needed.
It also helps when the undercover officer tactic has on occasion had significant results. Bob Lambert, one of the officers who fathered a child with an activist he then promptly abandoned, infiltrated the Animal Liberation Front and prevented the group from launching a bombing campaign against shops that sold fur. He also though, according to Caroline Lucas using parliamentary privilege, planted a bomb in a Debenhams store that caused £300,000 worth of damage.
The few cases that did provide useful intelligence or stopped attacks seem to have justified the placing of officers in wholly peaceful groups, and with it the relationships they then cultivated and often so cruelly broke off. The use of sex also seems to have been so widespread that it's difficult not to believe it was encouraged: after all, wouldn't that be a great way of allaying suspicion? Would spies go so far as to get into serious relationships with their targets? Justice Tugenhadt claimed MPs had authorised exactly that through their passing of Ripa, denying compensation to women who had relationships with officers, as everyone knows spying is just like James Bond, and Bond often bedded his glamorous fellow agents.
Is there anyone other than Theresa May or David Cameron then that imagines the inquiry by Derbyshire's chief constable Mick Creedon is likely to get to the truth? While it is at least being overseen by the IPCC, which under new head Anne Owers ought to be given a chance, we've surely moved past the point where the police should be allowed to investigate themselves. Under Labour it was arguably the case that too many inquiries were ordered, mainly as a way of trying to save ministers accused of impropriety. Under the coalition, we've had Leveson, and that, strangely, seems to have turned the government off the idea. You also can't help but note that while the allegations about the National Public Order Intelligence Unit deal with Labour's time in office, the claims about the Special Demonstration Squad mainly cover the period of the last Tory government.
As with the revelations about GCHQ, what we've seen is an example of how power is always likely to be abused. When it is, we need proper oversight and independent inquiries to ascertain what happened, how it happened, and how best it can be prevented from happening again. That means we also need politicians that are suspicious of how power is exercised by the other arms of the state, rather than happy to be servants of the rest of the bureaucracy.