Accident, what to do?

some nob hard working delivery man had parked lawfully stopped to load/unload his van in the bus lane and on double yellow lines

ftfy
Without seeing the exact location and time, it's entirely possible that the van driver had done nothing wrong, in spite of the double yellow lines and bus lane. I can think of one drop that I've done literally hundreds of times where I can lawfully stop to load in a bus lane with double yellow lines, as long as it's between 10am and 4pm. or 7pm to 7am.

So, in despite of the fact that you're a total bell end if you run into the back of an illegally parked vehicle, you might somehow have managed be an even bigger one because the van driver had every right to be there.