I would second the warped discs - is the kwik fit you went to a reliable garage, keepng in mind that they don't need to be warped much.
What type of pads do you have fitted? I know that some of the pagid/EBC pads, such as red stuff/black stuff can feel "grainy" when they are cold (because they are performance pads) - this could cause a vibration, though I wouldn't describe it as a judder...
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MX5 1.8 Sport
Might have the wrong forum here...