Wrong Altitude
Call me dim as a mere Piper driver but were ATC asleep ?? I would expect a call off Farnborough radar if I strayed an inch above 2,400 into controlled airspace.
To fly 5,000 feet too high ..... like that is a whole mile ... without anybody noticing for a whole 40 minutes is strange in the extreme.
Or was he flying proceduraly way out of radar cover and only a call that said ".. maintaining three five zero .. " caught him out ????
How did he get caught ???