A taxi driver acted in a psychotic manor toward me. Cannon St -> Tooly street

You're right to be skeptical of any punishment he might receive from the police. I got sideswiped by a BMW last summer, and even with his plates the police did fuck all.

Screw the rozzers, they'll give him a comfy chair for the afternoon and free tea and biccies. If the passenger complains though, he gets a black mark in the register book with the PCO who give him his licence to work. Three black marks, he loses his licence. So it effectively loses him his job.

Mind you, people having heart attacks can become completely beside themselves in that way - best you didn't hit him. A guy I know had a not dissimilar confrontation with someone, who dropped dead in front of him - without a punch being thrown luckily.

On the issue of self-defence, that comes down to your state of mind at the time of the incident - if you believe that you are about to be assaulted, then then you can legally throw a punch in self-defence, even if it's the first one. That's how the overpaid arrogant scouse thug managed to get away with punching someone's teeth out for daring not to hand him the volume control at a London nightclub when he demanded it. He just lied that he thought he was about to be assaulted and got off scott-free.