In another life I was an investigator for a UFO group and several of the cases I dealt with were explained by person(s) seeing aircraft at great distance. Joe Public is probably little used to observing such things so they can cause concern. An example was someone walking a dog in north London early one morning before sunrise. They saw a bright light to the southeast which slowly descended and then turned sharply to their right, gained speed and vanished. It turned out to be an aircraft inbound to Heathrow from the Lydd direction which "vanished" as it turned on to final approach.