Revell do an excellent paint remover called 'Paint Remover'. It's not cheap but a little goes a long way and it's not unpleasant either. Takes of many paints easily, including enamels.
As for acrylic paints, they will come off with surgical spirit which can be bought off the shelf from chemist shops. It's unpleasant to use and doesn't have a nice smell, but you can get a large bottle for a few pounds. I'd recommend protective gloves for that, not due to the unplesant chemical but the mess it makes.
Finish either method off with a non-aggressive household cleaner with a tootbrush. Rinse and let dry.