There is a wonderful (free) site, FlightRadar24, that overlays on Google Maps a real-time overview of what planes are in the world’s skies. It even has apps for your phone, so you can point at a place flying overhead and see what flight it is, and where it is going. It is just wonderful, and quite mesmerizing. When you click on a plane’s icon, a panel appears with the flight details, a picture of the plane and sometimes even trivia about the flight in question. If you click on an airport’s icon you can see information about the airport as well as details of incoming and outgoing flights.
Below is the view of England from the Midlands south and a part of western Europe at 3.15pm today. Click it to get the full effect. I do not think it counts military flights. Still, it is dizzyingly busy up there!