The Chilterns come quite close to London, the M25 motorway glances by their edge just where the HS2 works now are, one of a couple of places on the M25 where you can see central London (going over the high bridge at Dartford is another). I wonder which rail line gives the furthest vista, possibly only to the driver. It comes as a surprise to get a sudden view of it all from the Central Line Hainault loop way out by Chigwell.
There are formal "protected view" corridors in planning about St Pauls Cathedral from certain key points, such as Greenwich Observatory, Richmond Park, Hampstead Heath, etc. which have a notable impact on high developments in London. It's had a significant impact on Docklands developments around Canada Water. They apply both to the direct view, and also the "back view" of developments beyond the cathedral. There's a map of them somewhere.