I got curious and I made some estimates of the distance travelled in less than a second from when the Peugeot appeared and calculated that the speed was about 50mph and a little less at impact. I assume he was under brakes as the nose is well down. This means that if he started to brake when he blew the horn he was doing well over 50 on the approach to an zone with obvious activities taking place. To my mind he bears a good proportion of the blame.
I think many people don't appreciate that the stopping distance from 50mph is 13 car lengths, or 53 Meters / 175 Feet
and from 60mph is 18 car lengths, or 73 Meters / 240 Feet.
The other issue here is a very poor bit of road design with signage in what should be a lane that allows entry and merging. If the sign was placed before the break in the centre island the Morgan would have had a lane in which to accelerate and merge safely.
Don't get me wrong. The Morgan driver made a bad error, and it is lucky he didn't do it in front of the motorcycle that arrived on the scene 10 seconds later.