Gibbers, a friend of mine has a rear-facing camera built into a rear light. I can't tell which one I'm sorry. Doesn't help with a head-cam I agree, but is providing evidence to assist the police currently bringing a prosecution against the driver who, between exchange of words between my friend and the driver, then forced my friend to come to a stop, an a further exchange of words (with threats) entailed. Luckily for my friend, and independent witness was walking along this section of road and was, I think, using her mobile phone to record the incident.
When later confronted by the police about his actions, the driver refused to accept a caution, and so the police are taking him to court.
My friend made a miscalculation when enter the busy road form a junction, but believes the driver then deliberately sped up to squeeze through the gap between my cyclist friend, and a car waiting to turn at the junction. A punishment pass in other words, which led to the initial exchange of words.
So, get a camera.