chevvron:
You have a fair and valid point, but what I said was
"I would guess, no more than 1500 ft AGL."
with the emphasis on guess.
I have a reasonable familiarity with aviation and, in particular, with the traffic patterns at Wycombe, and this was a most unusual event. FWIW, I've had a little experience flying light aircraft and, in happier days, been a guest on the flight deck of 744s many, many times. I think I can make a fair guess at an aircraft's height -- but you are of course correct, it was a guess.
But if he was at 1500' AGL, he would have been at 2000'+ QNH which would be OK for transiting the Wycombe ATZ
I share your dislike of the "retired scientist" with the line on his window and the laziness of the press who love an easy story from a pseudo-authoritative source.
My local paper loves stories about people "threatened" by "radiation" from "telephone masts".