I did that jump in 1997!
When I did it I was the first with two friends going after. I was being pulled back to the walkway beneath the bridge as my mate, a ‘stocky’ fellow jumped and they played a trick on my friend who was to jump last.
As ‘Stocky’ bounced back up towards the bridge on his jump the guys underneath slammed a metal grid down with an almighty crash (out of sight of those on top of the bridge). The people in the know on top shouted “he’s hit the bridge, he’s hit the bridge”.
Oh how we laughed later! My friend jumping last incredibly took little persuasion to jump in spite of this, apparently he was ok when he saw there was no blood!