Thanks for the responses.
PuntoSaurus - that makes total sense.
toptobottom - now that you mention it the hovering is usually the turbines (noisy beasts
).
I live a stone's throw from Tower Bridge on the South bank of the Thames. As you say most of the singles seem to head eastbound curving north east, following the river. The views must be incredible. Sadly the closest I can get to it is as PAX flying into LCY (until I get my twin rating at least!).
London Bridge and Southwark are densely built up but I suppose the river is there as a failsafe option.