Reading through tehgrauniad's riots deep-dive, the impression that I get is that the whole "riots as an insurgency" idea wasn't that far off. I've been indisciplined in that I took notes but didn't keep links (a problem with paying for and reading the actual newspaper), so you'll have to trust me on this. Obviously, blaming the whole thing on "criminality" is about as useful as blaming rain on "water falling from the sky".
The first common factor that struck me was that pretty much everyone they interviewed had a grudge against the police. Not in any broad theoretical sense, but a grudge - a specific and personal memory of perceived injustice and especially incivility, cherished over time. Now, it's in the nature of policing as a public service that nobody enjoys it. If you're interacting with policemen on duty, it's either because they suspect you of being a criminal, or because something bad has happened to you. Generally, everybody would quite like to minimise their lifetime consumption of policing.
There is something that motivates people to put up with it, though, and that something is legitimacy.
The second common factor was the attitude towards property. Quite a lot of the people the Guardian spoke to reported looting goods from shops, and then giving them away, or witnessing others doing so. Stealing goods is one thing, but immediately giving them away is rather different and very much a political act. So much so that there is a word for it (and I'm not the only one to notice this).
Of course, police legitimacy comes in a very large degree from their role as protectors of property, so this was a way of directly challenging their claim to provide security and to employ legitimate force.
Eyewitnesses often described a tactical, practical implementation of this - small groups of rioters harassing the police, in a sort of screening or covering operation, while many more looted or destroyed property. It's very interesting that this could all happen so quickly.