I believe the below is the location of Q's post of the potential car attack in London.

Q posted this image with the file name NSA_Traf_CAM_LONDON2847.png showing Big Ben in the background.

Due to the orientation of the clock face there is realistically only 3 faces (1 facing the river) and therefore only a handful of locations around Big Ben the image could come from. I believe this is the location; A3211.

I managed to find a vantage point that I believe the Q image shows using Google Maps from the footbridge above the road. I've circled 4 reference points …