If its like mine, there is a large 50p size nut which encircles the back of the lighter unit. It is right at the end of the "barrel" which encloses the cigarette lighter stem, near the spade which the positive connector plugs onto. Don't search any nearer to the panel than immediately around the center electrode spade. The nut clamps the barrel to the panel, so the nut is not near to the panel itself.

The fusable link is a short 1cm connecting wire between the spade-connector and the lighters center electrode. You must remove the cigarette lighter unit to have any hope of replacing or bypassing it. I think it must be a thermal fuse to prevent melting of the plastic rear, but if you short out the lighter I guess it burns out before the proper electrical fuse in the fuse box. I just bypassed mine by removing the insulating washer between the spade and electrode washer.

Thanks to Cat for helping me work this out with jiggling of the cigarette-lighter which eventually made the nut come off in my hand The nut is thin metal and holds the lighter barrel on with more a springy action than tightness.