I don't have a ST but close, the Zetec, im sure the cars are pretty much identical in the pedal box assembly. A slight click has developed when the clutch is depressed, you can feel it slightly through the pedal too.
Google says that the clutch pedal meets a plastic arm that comes through the bulkhead, which pushes onto a tube on the pedal. I stuck my head under and this is correct, there is no circlip or anything retaining it though, the Ford clip seems to just fall off from what I have read, im sure putting a tie wrap around it will stop it working its way along the arm though.
I'm not sure where the clicking noise is coming from, if its from this plastic piece moving laterally on the clutch pedal arm, or the spring which gives the pedal some weight. Is the clutch cable or hydraulic (cable on last legs if its cable?).
Anyone else had this, seems moderately common, if so whats the best fix?