@AOG
Since when has having an argument in a public place been an arrestable offence?
Pending a video showing how the incident escalated from a casual "Excuse me, miss, but is this guy bothering you?" to a 4-officer, bundle the guy to the floor incident, I'd file this under (2), in your OP.
The article says he asked repeatedly what he was being arrested for but got no reply.
The video shows some conversation between him and the policeman who keeps pressing his head to the floor (in the video Tambo found) but the exchange is rendered inaudible because of the constant shouting by the girlfriend.
Article goes on to say he was put in a cell, in Islington but, later, released *without charge*.
Every chance his complaint will stand up.
Whatever was spat at 1:40 in Tambo's link, it moved too fast to be seen in mid flight and you cannot see where it landed on the officer. If real, I dare say there'll be a sample in an evidence bag…