ok i managed to get mine off. Taking off the lights was a failure, as well as removing the bolts that are visible at the rear of the bumper.
Pair of mole grips up between the bumper and the chassis. move it around till it hits something, then feed that somthing into its grasp. clamp on, undo bolts underneath. Fidgety as hell, but it beats rounding off nuts and dismantling bumper etc
Also another way that i got a bolt out with..... i used one of the supporting arms to lever the tow bar assembly down, causing more pressure on the none visible nut, and the bolt came out with relative ease.
hope it helps!