London is an amazing city and I felt it was worth flagging some resources to help you find the best London photo locations. Firstly its a big city and you can only cover so much in a day plus depending on where you are you will need to take care regarding personal safety. Also make sure you plane for good refuelling stops for elevenses and for lunch.
FREE - Photo-walks On LENSClof I have posted a number of London photo walks that are free and you can follow these to get to some great locations.
Hope you enjoy these however here are a few others to look at
Photo Locations You may be looking for something specific so here are some great resources to help you find the location your looking for On LENSClof I have posted a number of London locations OPEN
Here are several more worth looking at:
Try one of the Videos