I had "fluctuation of brake effort" as an MOT advisory for a number of years but couldn't feel anything myself. I wasn't convinced they were warped but replaced them with some Brembo Goldlines nonetheless and I've had no MOT comments since. They are better quality and lighter than the OE Brembos but £285 per pair against the £480 of the OE discs (2½ years ago).
Serie Oro, left - OE, right
Try Simon at WSC Performance who gave me a really good deal.
http://www.ukmonster.co.uk/monster/s...ad.php?t=56141
Before committing to replacements, I'd recommend you try Mr Gazza's "Italian Tune", which may improve things, if your discs aren't actually warped.
http://www.ukmonster.co.uk/monster/s...35&postcount=3