The US Coast Guard have an interesting site on GPS outages at
http://www.navcen.uscg.gov/gps/default.htm . Not much reference to foreign countries though. However, US jamming trials have a 'stop' option which I believe can be exercised by a pilot through flight service. Maybe the same is true here? "Shawbury, are you jamming GPS, if so, please desist" or something?