I think the treads at BMD South Stand are only 750mm. That gives enough space for 2×350mm steps plus 50mm for safestanding folding seat/hand-rail. However, according to the Green Guide, in terms of spacial allowance per row, that only equates to 1.3 to 1.5:1, not 2:1. I think the treads were originally going to be 800mm+.
1.5 sorry, aye, thats it