See attached photo.

Mine is at the back with a nice 30 millimetre spanner to do it up but the one to take off is round and the bar just spins round how am I supposed to remove it if my mole grips won't grab it I have no space what so ever

See attached

Use a 2 inch pipe wrench.

If that doesn't work ...try welding a piece of smaller pipe on wich you can use a bigger pipe to break it free.