Thanks everyone for the replies so far.
I think the best advise from the above, broken helmet means possible spinal injury.
The hospital asked to keep the helmet as evidence for their training, it was snapped in half.
We are doing a whip round to get the best helmet we can for the guy when he gets back on the bike!
And obviously first aid asap, then move up the scale.
Another injury picked up by another rider at another time, was branch down ear and perforated ear drum….