Twice, once in the 1980s camping in Wiltshire, DH and I observed a cylindrical craft in the sky at night. It had no lights and was flying low but silently. It circled the campsite and then headed away north. We both remember it.
The second time was on a regular flight from Morocco to the UK. A black cylindrical craft flew slightly below and to the left of our plane. Lots of people saw it and were calling out to each other to look. Either we overtook it or it vanished but lots of people asked the staff about it when we were leaving the plane in London but the staff brushed away questions. As someone else said, pilots often relate stories of strange things in the skies.
I remember hearing a BBC radio programme, some years ago which was a series of interviews with supposedly reliable people like policeman, EX-RAF etc who had seen UFOs and insisted that they were telling the truth.
Also, didn't President Obama allow the CIA (?) to release data about UFOs which were thought to be genuine sightings?
Have you seen one OP?