My condolence to the family of the man involved. A sad loss.
I have a lot of time in a Tiger and I have never seen anything like that. A very scary incident indeed. Unfortunately where the aircraft enters the spin is a little far from the camera. But it would seem he is in a medium level turn at high power. If I was guessing, he was accelerating for a fly past.
If you look at the windsock in the vid clip, it would seem the wind was not that strong. I know there are hills around that airfield that can cause some turbulence.
Anybody have any ideas here?