Been preparing this for the Driving Day on Sunday, which should be messy.
The brakes have been complaining a lot for the past few drives, so I stripped down the front brakes last night. There were stones trapped behind one of the splash guards which was the source of a lot of the complaints. The splash guards have now been modified to stop this happening - slotted to allow the stones to fall out:

I also found that one of the sliders on the carriers on each side had seized VERY tightly. Carriers came off and had a drill run down the sliders, then emery paper over the pins, nice big gob of grease put in and re-assembled.
Now stops much better!