Removing main chassis earth bolt Focus Mk2

[Powhatan]

I need to clean the main earth connection on the body. The bolt has a surprisingly small head (10mm spanner), which has merely deformed when trying to loosen it. I presumed that the nut (under the wing) was captive, and wouldn't turn when loosening the bolt. Maybe it isn't captive but it seems a challenge to get any kind of spanner/socket onto the nut due to the restricted space caused by the coil spring.

Is there a means of releasing the bolt (after I've filed the head back to shape), or am I better off getting a new battery earth strap and making a new chassis earth point away from the coil spring?

[dezwez]

try a pair of molegrips

[isetta]

so you can reuse the earth cable on a new bolt in a new hole, you could try drilling the head off the bolt (after centre punching middle to stop drill slipping off) or grinding head off with dremel type tool.