A nut splitter should get that nut off without the risk of any damage to the toilet.
http://www.toolstation.com/shop/Nut+Splitter+Set/p80007[/QUOTE]
You use them with impact guns, trying to split a nut like this with them manually, would split the pan in half.
Nah, you put a spanner or ratchet on the bolt head on the end of tool. Wind the chisel point into the nut - it splits - job done.
You've obviously never done the void bushes on a Cortina.