Acid Rain on cheap lacquer i reckon Nick, has the car had any paint? are all panels marking up uniformly?
Seen something like this type of contamination before, and turned out to be the brake dust off trains, settling on the car during the day, while parked at a train station car park, day in day out, lacquer would eventually break down, especially at high humidity times if the year...
I have also seen this type of problem, reappear after painting!!
Thom