I found a different method worked for me to get the bottom (metal) bush released - no grinding or raiding the freezer needed. Get hold of as big a Stillson wrench (aka pipe wrench) as you can find. I used an 18" one, but longer might be useful if you can get it. It probably helps to spray the bolts a day or two beforehand with your favourite penetrating
Assuming you've got the back of the car jacked up and well supported, the roadwheels are removed, and the rear wheelarch liners partly loosened and folded out the way, proceed as follows.
1. Undo top mounting bolts on each damper. Socket onto the bolt head in the wheel arch, ring spanner onto the nut at the back to prevent it turning, then apply your muscles (or cheat with air tools…). The side of the car with the fuel filler flap is fiddlier, because the fuel filler pipe runs near the nut and there’s less space to get your fingers in, but nothing too difficult so far. I found that the bolt head and the nut are slightly different sizes – 19mm and 17mm, I think, but I didn’t write it down at the time, so double-check for yourself!
2. Undo bottom mounting bolts. Bottom ones are bigger (can’t remember socket size, maybe 21mm?) but access is easy and fortunately mine loosened fairly easily with an extending wheelbrace for leverage. There is no nut, as they screw into a threaded hole in the lower suspension arm.
3. The damper is still stuck onto the lower suspension arm because of the Dreaded Metal Bush (DMB). Grasp the upper part of the damper and pull it downwards to compress it. When you’ve made it short enough, rotate it downwards and let it dangle towards the ground.
4. The bottom of the damper has a metal ring welded to it. Inside this ring are a rubber bush and the DMB. Working from the wheelarch, use a hammer and cold chisel to knock the metal ring off over the rubber bush. Give it a few taps moving the chisel to various points around the metal ring, and it should come off without any problem. You’ve now removed the main part of the damper, and left behind the rubber bush and DMB.
5. Get rid of as much rubber as you can from the DMB. Some might come off during step 4; I either chiselled or used a junior hacksaw on the rest.
6. You have now exposed most of the DMB stuck tightly in the lower suspension arm. A tap with the hammer at this point might help crack through any corrosion between bush and arm, but don’t try battering it to death or you risk damaging the suspension arm.
7. Put your Stillson onto the DMB with as tight a grip as you can get, and then heave! It should bite into the metal (hence getting rid of the rubber bush) and with a bit of luck the DMB will turn in its mounting hole. A bit of help from the hammer on the end of the wrench may be needed to get it started. Keep re-positioning the wrench and turning a bit each time, and the DMB should start to work its way out the hole. You should then be able to wiggle it out by gripping it with pliers.
8. I cleaned out the mounting hole and put a smear of copper grease into it before fitting the new dampers: might help next time.