That's why....
Omg what a **** off #Thunderstorm - wow!! All #Heathrow fligh... on Twitpic
Excuse the comments at the bottom of it, but those brave pilots (2-3 of them that went through that bugger where brave, most decided they didn't want too - I know that!
I could feel the downdraft rattling against my window, at about the same time that the aircraft on approach pulled off there approach.
If you look at
Met Office: London & South East England: latest radar - it was near enough a downpour.