Yup, I initially used an adjustable wrench - I bent it easily; to the point where it won't adjust anymore.
So I invested in a decent 32mm spanner. It's almost 2ft long, obviously not long enough...
The gist here seems to be more easing oil and an even bigger length of scaffolding! Unfortunately my new spanner has 32mm ring on the other end so getting a bar big enough will be a pain.
At least I now know they really are that tough to unscrew :)
Cheers Rich H