Not that it's now especially relevant to this thread but I've now had a close look at the handbrake mechanism at the caliper end and it looks quite well engineered really. I still plan to keep it all clean though. The brakes on my PHEV certainly creak and groan a bit like an old ship though, especially the rear brakes when the handbrake is applied (maybe I keep them too clean?). Don't think I've ever experienced that before on any other car.
I actually have a low mileage, part worn Toyo R37 spare tyre (just the tyre, not a wheel as well) that I take on long journeys, just in case I get a terminal puncture (the last puncture I experienced was a large gouge/slash on the side of the tyrewall that couldn't possibly be repaired. No idea what caused it). I believe it's not always easy to find a Toyo R37 at short notice. I paid £50 for it from a tyre dealer. I cleaned it and wrapped it in cling film to preserve it. A sort of mummification. It doesn't take up too much room in the boot and can be filled with stuff in the middle. I have it strapped down with tie-downs as I wouldn't want it to project itself forward in the event of emergency braking. Mind you, I'm not sure how robust the tie-down hooks are in a PHEV, looks as if they're made of plastic to me.