[Arran]

Is it Bakelite or is it a polystyrene cabinet? If it's Bakelite you can wet sand the scratches out to some degree, but sometimes you can sand through a top layer into a rough and pulpy core. The the case of polystyrene the plastic and it's colour is consistent all the way through, no matter how much is sanded off. That being said you don't want to take too much meat out of the cabinet if the scratches are really deep. You can start out with 400 or 600 grit, (Bakelite is harder then polystyrene) then to 800, 1000, 1200, and move up in the grits until you hit 1500 or 2000 grit, then you are into polishes.
Regards
Arran