There is a somewhat radical way to possibly do it Rob, but I'd try it out on a hidden or unimportant area first. Very lightly paint on some brake fluid and leave it until the paint starts to bubble. When the paint is then seen to begin lifting, peel it away, and rub off any remainder with a cloth, wearing disposable gloves to avoid skin irritation etc. Dry off all the remaining brake fluid, then submerge the part in a strong solution of water and detergent (dish washing liquid soap). Wash the part thoroughly afterwards and, if required, polish it with a soft cloth.
Some paint strippers will do the job, but they may attack thinner areas of the material, or give it a slightly coarse, dull surface. Most, if not all of this can be restored using a plastic primer, available in aerosols from car parts and accessory outlets.
If the stripping doesn't work, then a very light rub down with fine grit paper, followed by successive coats of the above primer, to build up a smooth, even surface, should work. I can't guarantee success, but I used to do this fairly often on my rally car years ago, and it worked quite well.