Hmm, the Glasgow Spinal Injuries unit trying to be representative of the whole UK?
Funny as having spent 4 yrs working in the Sheffield SIU in the late 90's, only a couple of pts were from diving and only 1 ever from biking (not MTBing).
Top was motorbikes (also very good for serious brain injury) and cars, horses were quite popular along with falls from height (usually ladders or roofs), gliding and hang gliders were quite popular and some rugby players. Even had 2 pts (both adult) with broken necks from bouncy castles.
So all in: 8 MTBers in 5 yrs for one medium sized SI unit would appear quite an increase, but in the grand scheme of things still a drop in the ocean of hours and people out on bikes doing stupid things.