About the location
The area around Big Ben is definitely one of the most touristic areas of London. Nevertheless you shouldn't miss this place as a photographer, because there are quite a few great photo perspectives like the typical view from the bridge towards the tower, usually during blue hour with some passing cars or double-decker buses to get some light trails within your image.
Another great spot, especially during rain, is across the Westminster Bridge. There is a tunnel on the right side of the bridge you can use to frame your photos, which is a great place during rainy days.