Irish Air Corps PC-9 zipped over me earlier - I could hear but not see it, despite a clear sky and some cirrus which I thought might have made it easier to see, but I guess a pretty small spec at about 25000' - an Air France B777 appeared to be below the cirrus at the same time. It seems to be returning home from Zurich or Stans. IAC PC-12 just crossing the Channel on the same route...