A few years back, I was out in my garden (West Berks, UK) one sunny Summer Sunday afternoon, when I heard the sound of a heavy jet approaching, but low (we see lots of TMA arrs/deps etc around here, but the base of CAS is around FL45-55 depending upon exactly which way you look).
Seconds later a United 767-300 came into view and passed W to E at (I estimate) around 2000'.
Ran for the scanner, and found him talking to Farnborough LARS.
He was routing back to LHR VFR after a flypast at an airshow at Middle Wallop (so non-rev I assume). Had to be given climb E of Reading to get into the pattern!