London is a great city for photography. Here are my top 3 best places to get an aerial view of the London skyline. Best of all they are all free.
No 3 View of St Paul’s

Just across from St Paul’s is the One New Change shopping Mall. Take the lift to the top floor which is a roof terrace with some bars. This gets busy so has limited access at popular times.
No 2 Tate Modern

This is a great view a 360 degree walk around. Go to the basement and get the lift to the top.
No 1 Sky Garden

This has to be booked in advance but is well worth it. The top of 20 Fenchurch Street which is know as the Walkie Talkie Building. The top floor is an indoor park with restaurants and a cafe.
Here’s a link to the website: https://skygarden.london/sky-garden-home