My auto does this too. On reversing and lightly touching the brakes. I am convinced it is from the front discs though. Cannot be the rear drums as it only happens if I touch the brakes.
Bob 10MY (Sept 09) TD4 HSE Auto in Stornoway Grey (Now Gone)

08 FL2 TD4 SE Manual in Rimini Red (Now Gone)

That's exactly the same as mine was. I'd read it could have been to due forward wear on the brakes but LR said it must be dust in the brakes. The final verdict was the handbreak. I've not properly tested it yet but they've taken about 1/3 of the travel out of the handbreak movement itself.

I will check the parking brake adjustment - there is certainly more travel than on my previous FL2. 10MY (Sept 09) TD4 HSE Auto in Stornoway Grey (Now Gone)

08 FL2 TD4 SE Manual in Rimini Red (Now Gone)

I had squeak both when forward and rear after new brembo discs and ferodo pads was installed. I thought that pads do not match the discs and changed the pads to brembo as well but the squeak was still there on low speeds, when parking etc. After couple of months I solved this problem. The two slidings pins on tha caliper was dirty and caliper it self didn't move free from side to side. These pins can be changed to new but I didn't have time for shopping so took an angle grinder with wire brush and cleaned these dusty dirty pins till they got shiny again, put some grease on them and no squeak at all. Caliper now moves free from side to side.

Try putting a small Chamfer on the leading and trailing edges of the pads.

This works every time on my Discos.

I fixed this problem by using my air compressor airline to blow out excess brake dust from both sides of the callipers on all 4 corners at no cost. Quick and easy fix for mine.