One does not need transit visa for
London, Amsterdam, Singapore, Milan or Moscow ....
But its needed for Paris, Zurich, Frankfurt ...
If u are changing airports in London, they will give u a 24 hrs transit visa right there ... so no sweat ...
I had the same issue in July when I was flying for my interview and had done a research on this ... I wanted to fly Delta, Swiss Air, Air France or Luftansa but after talking to French and German consulates and airlines, I decided not to go via them ... so I finally flew KLM ...
Talk to the consulates and the airlines for the latest info ...