This just goes on getting better. Welcome Clive!
After all the high tech stuff I have a much more prosaic question. Looking out of my Devon window this morning I could see aircraft streaming up the channel, and by checking their positions on Flightradar 24 (sad, I know) I know that I can see craft at fl350+ nearly the whole way across the channel, so it occurs to me that I should have been able to see AF Concordes on their way into CDG, but never did (although I certainly heard them). Would Concorde have been visible from the ground at cruising height, and would it have left contrails?