Could you please add a bit of explanation as to why you are so confident that this interpretation of the role of the police should be regarded as categorical fact?
Particularly in the case of UK, if your knowledge allows, given that we operate, at least in principle, an explicitly Peelian system of policing, in contrast to, for example, our European neighbours.
Consider the UK police treatment of demonstrators. It's one of the most brutal in Western Europe, and in many countries the very idea of a practice like kettling brings out images of fascist dictatorships.
I'm Norwegian. In Norway, government officials are often found participating in May day demonstrations, and it's a public holiday. Imagine my shock the first May day I experienced after moving to the UK, with police lining up units on horseback with shields all around and slowly forcing demonstrators into a smaller and smaller space and keeping them their for hours.
How does that fit with Peelian principles to you? It's the kind of method that is pretty much designed to provoke violence and distrust.
I too think that kettling is provocative and unnecessary. There is a balance that we have to strike as a society between, on the one hand, protection of property and freedom from violence, and on the other, freedom of speech and expression.
Personally, I would rather we allowed more of the latter at the (potential) expense of less of the former, perhaps with some civil compensation scheme for any who might be affected.
I also think that we should allow much more disruption than we currently do - that is often one of the ways protesters make themselves heard. If protests were allowed to make more of an impact then people might feel less inclined to cause trouble. Unfortunately any impact on the great economic machine is seen as almost taboo in some, rather influential, quarters, which makes moves in that direction less likely.
Another part of the puzzle is community leadership, whatever 'community' means in the particular context. The leadership doesn't need to be centralised, but if people don't engage with the police in situations like that then things can get out of control. Though again this is another area where I think the police are often at fault: following orders rather than engaging with people.
All that said, I don't agree with madaxe's statement: "(the police) are categorically not there to help you. They never have been.", and to be frank I don't see how your example shows that it is so.
Particularly in the case of UK, if your knowledge allows, given that we operate, at least in principle, an explicitly Peelian system of policing, in contrast to, for example, our European neighbours.