Ahh.. but apparently you should not believe everything you see on a radar. Some years ago I had the doubtful privilege of showing some ant-noise people round Heathrow Approach. They were blabbing on about aircraft regularly flying down Windsor High Street at 3-500 feet and I attempted to re-assure them that the actual altitude was more likely to be 1200-1500ft, as clearly indicated on our SSR labels. "Poppycock", cried the leader "You people can just change those settings at will to confuse us". Unfortunately nothing any of us could tell him would convince him otherwise.