Yeah, that's where I was looking - amazing how sometimes high aircraft really don't show up unless there's a white line with an arrow pointing at them. Actually, one of the Heathrow inbounds was trailing loads of vapour earlier so maybe moisture in the lower atmosphere and the lowish sun conspired to hide the monster.
Noticed a USAF C-17 go right round the houses yesterday: took off from Rota, N across Spain to the Lizard, NE, passing over London to Clacton, across to The Netherlands and down to Ramstein where, after a brief hold at 21000', it landed. Curiouser and curiouser...