Like any large town, the meaning in your dream depends on whether you have lived or visited London. To understand your dream then you will find it useful to read Associations Working With
Example: I was in an area of flats, like in London. I realise that I have been in this dream area many times before. An old man, rather Merlin magician type, lived in an open area near the flats. His house was disguised, rather like camouflage on the outside.
Example: Dreamt I was in London and flew from somewhere near Fleet Street. I flew toward the river and saw lovely streets, old but attractive, with many interesting shops. Flying on I came to the river thames itself, huge and wide. I landed in a street full of open fronted shops, like a market. I felt what a wonderful place London was – so varied and full of life and creative trade and people.
Example: The war was on. I was in London. I drove off in a Jaguar car that I knew was not mine. Bombs had blasted buildings. A baby had been injured, and an elderly man with black hair (father?). He had a piece of shrapnel in the lower abdomen, and two men were trying to help him, sitting him up. I rushed up and looked at the man, telling them not to give him any water. Then I asked them if they had phoned the doctor or an ambulance. They said they had.
The dreamer had lived during the war, and after it finished had seen the damage in London, where whole miles of buildings had been destroyed. So the injured baby was probably a trauma he had experienced.
Useful Questions and Hints:
What was happening to you in the dream?
Where any memories involved of being in London?
Did you have any preconceived thoughts about London that shaped your dream?
Quite a number of Americans do not have any sense of where London is and what it is like.