These are probably the diffusers and they can be cleaned to some degree using normal cleaning agents (heard somewhere that toothpaste can be used). Getting at them is tricky but on a Mk 1 you can unclip the headlight lenses (be careful doing this as a cracked headlight lens starts to make this fix expensive!) and pull them forwards sufficiently to gain access to the plastic diffusers inside. Though fixed by lugs, these come out quite easily (getting sufficient purchase on them to clip them back in is a little trickier). Thanks to Ford's outstanding build quality (!!!) you MIGHT have to unbolt the upper front fixing for the wings to gain an extra couple of millimetres clearance to get the lenses sufficiently forward to get at the diffusers.
Nic davies, March 2008