[Red Herring]

This sounds like a pretty horrific experience and you did well to stay on the bike under the circumstances. Have you any idea as to what provoked or caused the driver to do what he did? Given what you describe I'd be as disappointed as you are that the police are not going straight round there and looking into the incident, however before people write off an entire profession I think they ought to sit back and consider what they have to contend with here. Road rage incidents are incredibly common, I'm not saying they are acceptable, just common, and the police receive thousands of complaints from drivers about the actions of another. Unfortunately they are extremely hard to investigate because there are only two things that all drivers have in common, they all make mistakes and they all think they don't. Add to this that there are very rarely any independent witnesses and what you end up with is two different accounts from the drivers involved, both blaming the other, and no way of finding out the truth.
What makes this incident different is that there was contact and therefore potential for supporting evidence, and also the difference between the vehicles involved would tend to support one side over the other (He would have trouble arguing that you reversed into him three times), hence my disappointment that they have not taken your report more seriously. Unfortunately most Forces have policies about such things, and at least one force I know of will take no further action over allegations of bad driving unless there is an independent supporting witness, but I'm not sure about the Met.

They do however have different policies around the investigation of an alleged crime. When you reported it did you report it as a road traffic crash (RTC) or as a crime (criminal damage/assault)? It would make a substantial difference to their process.