Having tried many things to strip the paint from plastic or metal Warhammer Figures, I have eventually been shown the way forward, and thought I would share it with you all, especially as I have seen some unscrupulas sellers trying to sell this information on ebay!
There are simply 3 things you need.
1. A bottle of "Fairy Power Spray" make sure you dont mix it up with Fairy Washing Up Liquid, as this wont work, its Fairy Power Spray, it comes in a green bottle with a red lid and contains 375ml for around £3-£4 from most supermarkets, I get mine from Asda.
2. An Old Toothbrush.
3. An old plate, bowl or similar container.
To strip the models simply arrange then on your plate/bowl and turn the nozzel of the Fairy Power Spray to on and pump/spray it all over the model you wish to strip of paint, making sure it get a good covering with the spray, spray from around 8-10 inches to get a nice foam going. You can strip as many or as few as you like in one go, this stuff is perfectly safe and wont melt plastic or metal models, it can be used on all sorts of models, including larger items of scenery or tanks.
Next leave them to soak for a couple of hours, I find this is long enough to lift the paint off, however if left over night, it will also soften glue, which if your wanting to do is excellent, you can completely strip the model down to its bare components.
After a couple of hours take your old toothbrush and give the models a good scrub, the paint will just come away, pay particular attention to areas where several layers of paint may have collected, in creases etc, then simply rinse off, and there you have it, one brand spanking new miniature ready to paint, with no loss of detail on the model what so ever.
Remember though this stuff can be an irritant to skin, so if you want just use a set of marigolds! and wash and rinse your hads after, along with your old toothbrush.
I have managed to grab a couple of excellent bargains from ebay of some very poorly painted models, and managed to strip them back to new in a few hours.
I hope this helps