Well if TPS are the cheapest I'm selling the car
Front pads with discount are £147.46+VAT
Front discs with discount are £87.44+VAT each
So the total is £386.81
Now for the interesting bit... 
I pulled the near side apart to inspect the pads, the off side had a broken wire last winter and the sensor wires were joined together so I knew it wasn't that side that was causing the problem.
There is still 6.5mm-7mm of material left on the pads, however there is a small lip on the disc and the inner lip has cut the sensor wire causing the light to illuminate. My initial thought was to change them, but with 6mm of material I feel it is a bit of a waste.
The discs and pads are all genuine Audi parts and I suspect original as the car has only done 73k and the person I bought it from was elderly and certainly not a fast driver. I am now left wondering if Audi err on the side of caution with the sensors, my Mercedes never showed a light until there was 2.5mm of material and even then with spirited driving another 1000 miles could be easily done without any problems.
Genuine Audi pads....most likely original
This is the groove and sensor cut by the lip on the disc
6.5mm-7mm of material left
Evenly wearing top and bottom
So I have joined the sensor wire and rebuilt it and will fit new pads and discs at a later date