You're right Rob, although I'm not sure a claim must be made withing 24 hrs. I've put claims on paper MONTHS after the accident happened (always because the two parties tried to settle the dispute between them at first and in the end one of them doesn't keep his promises)

You're right about him being wrong when he was overtaking the cars, but worst case scenario he'll get a fine for that (if anything).

Bikers can suffer subtle head and neck injuries which only come to light many months later.

You're not wrong there..this makes me think about an accident I was called to last year. The initial report by the call-centre was : "head-on collision between two bycycles". By the time we got there both men were dead. They both hit their heads on the sidewalk...

Or an accident I was called to a few months ago. A driver of a just-parked car opened up his car door without checking for bycycles. A lady on a bike that was just passing by swings around the car door, looses her balance and falls onto the ground. She has a small wound to her head, nothing serious it would seem. She is transferred to the hospital by ambulance. We follow the ambulance to the hospital, where I take the lady's statement down.
The end of that, and we continue our shift.
Several hours later when I'm about to end my shift my boss comes up to me and says : "better finish that report quick, that lady just died". It turned out that headwound was much more serious than was thought at first.

So yes, ALWAYS go your GP after you've been into an accident, even if you don't feel anything at first. (especially if you've had a blow to the head!). All the rest is far less important.