The rear pads are the worst offenders but thinking of some of the cycling I have been doing there might be a valid reason. I have been on lots of long 50 + mile rides, many at night where I have had to cycle down very steep hills. Not wanting to freewheel - especially as there has often been traffic on said roads - I have been forced to feather the brakes to keep things safe and controlled.
Regular maintenance of ones Brompton ensures that these things are picked up early. I will be fitting a pair of pads to the rear of my Titanium Orange Brompton in anticipation for the Richmond to Oxford ride on Saturday.
I am going to look into getting some pads by Swisstop as they come highly recommended. Evans Cycles also sell some pads that fit a Brompton and having had a pair that were pretty good too. In the meantime I'm sticking to the official Brompton pads that gave so far served me very well.