I don't know about London, but where I live we have easy access to three major airports and a number of civilian ones. Above our home there always seems to be low flying aircraft of varied shapes and sizes at various slots in the day. Looking at the sky patterns, you often wonder if the aircraft behind is following the one in front!.
We did have an incident a number of years ago, when people found their property and ponds with a covering of a 'oily like' fluid droplets early one morning. Suspicions were laid on an above aircraft, but the final answer was never released, and is now a forgotten event of the past!.
We don't get many airliners over these parts, but I just had a eurofighter fly over head at low altitude and incredible speed, we often have them fly over, not sure where they're going but it can't be far away, I've tried looking on Google Earth but the only nearby RAF base showing is in Northumberland but that's in the wrong direction.