EBC yellowstuff pads, and grooved/dimpled discs for the front, I would concentrate the money on the front, if that's all you can get for £300, but this should I would imagine get you yellowstuff front and rear with grooved/dimpled discs, your best VFM improvement will come from the pads, then the discs, if only grooved that is ok, if only dimpled that is also ok, these sharp edges serve to keep the pad surface clean of glaze by constantly de glazing on every brake press, if money left over get some braided lines.
tabetha