Well I bought myself a set of these:
In essence its a normal socket that fits on the end of a ratchet with spiral teeth with a reverse thread.
I soaked the bolt with penetrating fluid and after about a minute or 2 of swearing and cursing, the bolt finally gave way. I have no idea how strong the booga was who put this on - I'm hardly a svelte chap and it took some effort to release.
Having looked at the damage I had caused to the bolt, its actually a very soft metal which I found strange.
Oh well, just need to get a new bolt now...