Tone, it is possible to DTI a brake disc. You attach a very accurate measuring device to a fixed point on the car, then place the 'probe' on the disc, then you spin the disc and it will tell you how far the disc runs out, it is incredibly accurate. We can do this.

As you know, the AP rotors are over £200 each, so fingers crossed its not that. Also, I'm not sure if I would replace them individually either.

I will see what I can find out regarding the pads. Can you remember the caliper number? Or failing that the part number of any of the pads you have had in the past for them?