It's most likely caused by the pad material, or the discs have become glazed because of the pad material. Howard Reynolds of Race Brakes recommends TRW, which is a commonly found brand of pad or his own Race Brakes brand pads.

IT IS hard to diagnose problems like this without seeing the car and experiencing the problem first-hand. But the fact that changing the fuel pump hasn't fixed anything suggests its not a supply problem. I would look for an electrical fault, possibly even a loose or faulty connection. It could even be a problem with the ECU.