Mike Tee. Durham and Newcastle traffic in and out via OTR will change squawk three times in quick succession. Outbounds will have a local squawk for Durham or Newcastle radar, then a Swanwick Military one to work them through the class G airspace, then the Orcam squawk when working Scottish. Vice versa for inbounds. It's so the relevant controllers have the squawk converting to the callsign on the radar screen.