I tried to open the bonnet on my Stilo but snapped the latch off.
I've been trying to turn the damn thing with a pliers, but no joy.

Is it a case of whipping the plastics off? I'm hoping there's a wire to pull in there somewhere?

if your talking about the one in the foot well then just unscrew the philips head screw (i think there is only one) then take the wire out, you will be able to open the catch then with some plyers.
I changed mine only in december, cost me about £20 for the whole unit from ebay. Mine was just turning without actioning the cable.