So after I witnessed a bad off a while ago I started to do some digging to improve my ability to be useful in those situations. This is by far the best resource I’ve found.
http://www.molenda.com/accident.html
Feel free to contribute / comment 
Bike safe include this. Basically the advice amounts to making enough room for an ambulance to arrive and leave the casualties alone.
I haven’t done any of the courses, but isn’t there anything about safety? Life saving first aid…?
No, you are advised to leave the casualty alone unless a trained first aider as you could do more damage. The only time you intervene is if the casualty is choking and you can unblock the airwaves safely.
If an untrained person moves an injured person with back injuries you could do more harm than good.
That’s about all they say about it on the bikesafe course other than making it easy for the emergency services to get to you
First bike on scene or equivalent
Biker down courses run for free by various fire brigades. I did the Kent one in Ashford maybe a couple of years ago with Jim who I believe set the whole thing up.
https://www.facebook.com/bikerdownuk?ref=stream
https://www.facebook.com/kentfirebike?ref=stream
http://www.kent.fire-uk.org/default.aspx?page=1397
A few of us rode down for it in Ashford, I’m sure there will be a thread on here somewhere if you search
Thanks Mark that’s excellent.
Sam, in most instances that’s probably advisable unless the casualty is not breathing etc.
Oh and the bit about how to detect shock is very good also. Reading that now and looking back I could have done a lot more without disturbing his neck / head / back. I understand not taking the helmet off and dragging them around the road etc but there’s something wrong if you can’t pinch their fingernail without disturbing their neck.
Okay. I can see that you need to have basic first aid and yeah don’t ever move the casualty - unless he/she is in danger of sustaining more injuries ect.
But when you call 999 they will ask you a lot of questions to assess the person and tell you how 
Another shout for the Biker Down courses - very useful highly recommended. They did show us some very basic first aid and how to remove a lid safely. However, most of the motivation was really geared up in being first on scene to gather info on what happened, see how many casualties there are (is there a pillion in the hedge unseen?), maybe before they go down hill, unconscious, can’t remove a lid themselves, can’t tell your where they’re in pain etc, leaving paramedics trying to second guess their potential injuries. It’s also that reassurance element, delegating tasks to others on scene, handing over to the pros lots of useful info, and not becoming an casualty yourself when the next truck comes round the bend.
Surely no 1 response should be to immediately dial 999. If it turns out it’s not an emergency - can always call them again.