At least so far as police forces are concerned, they can't really be reformed.

That seems pessimistic.

For one thing, any organisation made of real people is in reality affected by the views of those people. Even if there are some bad spies/cops/soldiers out there, a lot of people who get into that line of work do do it for the right reasons and because they genuinely want to make the world a safer place. If very bad things start happening, none of these organisations is going to universally side with a government that is doing those things.

For another thing, any organisation that requires funding is subject to influence by whoever funds it. As long as someone has to pay PC Smith's salary and there is enough civilisation left for essentials to require money to buy them, PC Smith is going to be accountable on some level because he or she literally can't afford not to be.

For a third thing, any organisation that enjoys special privileges that most people do not have, for example greater resources provided by the state or powers to do certain things legally when they would otherwise be illegal, is always under threat of having their special status revoked. The natural order is that everyone has the same rights and powers and resources, and the only ways that change are either through democratic acceptability as with policing by consent or through an actual dictatorship/police state scenario. And for reasons 1 and 2 above, it is highly unlikely we would ever actually reach the latter, which means the only way the police and security services get to keep doing what they're doing (and the only way the politicians get to keep their jobs) is by maintaining sufficient public support and trust. As we've seen in recent elections, there isn't a lot of that going around lately, so it seems unlikely that anyone wants to rock the boat unnecessarily.

Finally, it's worth remembering that we're talking about Britain here, which means the police very much isn't a paramilitary force in the way that many other countries have. Neither our citizens nor our police routinely carry firearms, for example, and while there are certainly specialist units in the police that do have that kind of equipment, they don't have anything like the numbers or equipment to put down a serious popular revolt. At the end of the day, there are still only 150,000 or so people working for the police, out of a population of well over 60,000,000.

This is why I think we're still a very, very long way from the kind of brutal dictatorships and police states that some people in the world still tragically live under today, and why I think despite the flaws of our various government organisations and the need to be mindful of their power and restrict it appropriately we are still a long way from any point of no return in terms of the balance of power between the state and its citizens. We've just let paranoia after a few high profile but actually relatively minor incidents tip the balance too far towards authoritarian tendencies in recent years -- which is, after all, why it's called "terrorism". At some point, we as a society are going to realise that this just plays into the bad guys' hands and stop putting up with it, and the balance will tip back again.