definately front and back ,reduces articulation a bit off road but gives better road handling,so much so that disco 2 uses ace which is a way to increase effect by tensioning roll bars
I have a Disco S1 on the rear and a 130 Defender on the front of my 1995 110 Wagon. Makes a huge difference on the road. Much less body roll, although tends to slightly under steer, but much more positive to drive.