I once flew regularly with a 1000hr ppl, on a trip north we were on track to overfly the Waddo MATZ @ 3800 on the QFE, on speaking to the controller we were asked 3 times to confirm our height, the controller then advised us of a "Heavy 8 jet" in our 3 oclock tracking 270 @ 2000ft QFE. A quick search for the camera and a shot of a lifetime. Wasn't difficult to spot with all that smoke out the back.
PM