Thanks Bill. For North American flights, I use Flightaware.com, and/or the StarAlliance electronic route timetable (for Air Canada). With these two sources I can get actual routes, altitudes, time of departure, aircraft type and callsign. It seems this kind of info is hard to come by in the UK.
Then please, sir, enlighten me; what is the best source of callsigns for British Airways? (this was the basis for my original question!)
Al