jtype Try this:
Flightradar24.com - Live flight tracker!
You can choose the area to watch in the top RH corner and also move the map by holding down the left mouse key and dragging it. Flight Radar will show many flights but not all. Military flights as well as some other types of flight may be blocked but most commercial airliners flying the airways system will be displayed.
The routes flown on regular commercial services can vary, particularly those flying over the Atlantic where they will take advantage of upper winds. So one day you may see many flying westbound and next day you may see fewer.
HTH