Courtesy of Benjamin Elliis I saw this WebTrak site which shows arrival and departure air traffic into London Heathrow. Other pages show similar for other London airports - Gatwick and Stansted
Fair warning - it's addictive.
I watched a replay of LX359 (the green plane which has just taken off in graph below - click on graph to enlarge) headed to Geneva GVA till it got to about 17,000 feet near the A10 exit for Worsham. A few minutes later AF 1381 headed to Paris CDG passed those coordinates at about 14,000 feet