I can see that what you're saying is capable of being true - if the abusiveness was really really severe - but even then I doubt any police officer or judge would wish to charge or convict, except in the most extreme circumstances.
I don't think the Public Order Act was designed to stop people being moderately rude to people breaking safety-related criminal laws. It is a vague law with wide discretion and it's used to stop or condemn serious harm only. Telling someone rudely that you're angry at their breaking the law isn't a serious harm. For many it is a commendable act of civic virtue. I don't see why we should wait for criminals to be put in the stocks before we throw fruit at them, figuratively speaking. In fact public opinion of society at large, should surely be the first force which compels people to obey the law, rather than the courts. The courts can only prosecute a tiny fraction of crimes, largely to set an example to everyone else. It's wrong to ask them to do all the work, to say that 'moral guilt for breaking important rules of society is only ever properly apportioned by a court, and that until it makes a ruling of guilt, we should all be respectful, and afterwards too, because a criminal conviction is the only proper public blaming mechanism for harm-risking or harm-causing crimes'.
Of course if you, like many, believe that we should prosecute people only when their safety breaches result in an actual death or injury then you'd have a different view, because you'd think that driving while using a mobile isn't truly "criminal" unless someone is injured. Ergo, if there was no truly "criminal" act by the driver then there was less of a legitimate excuse for anger from the cyclist.
+ I'm afraid that you can't be said in law to have caused a crime by being rude to someone - the chain of causation is broken by the independent voluntary act of the violent van driver.
