At One New Change shopping mall.
Once inside, take the lift to the 6th floor, go left out of the elevator, then left and walk to the edge of the viewing platform. You get an uninterrupted view of the dome of St. Paul’s Cathedral. To its left, in the distance, see the London Eye, through the centre of which you can see Big Ben. To the immediate left is The Shard.
To get there, walk to the left of St Paul’s Cathedral, passing the original Temple Bar on the left . Keep walking ahead, cross over the next road and enter the shopping mall.
I found this info on [http://www.londondiscoverytours.co.uk/7-days-in-london/] where there's also lots of useful info for Londoners and visitors. (I'm a Londoner but didn't know about this until just now.)
The site also has a list of film locations and of pop and rock locations too.
