Thanks, I was looking for that. Interestingly the area under the pitch is untouched, presumably to save time and money and because it can always be dug up later, if necessary.
Just looking on Wikipedia and it mentions that the stadium could be extended for rugby, and paid for the pool stages of the rugby world cup, and paid for by the IRB. It's the first I've heard
http://en.wikipedia.org/wiki/St_Mary%27s_Stadium