I didn't say it wasn't.
But it is also a public highway. ... photography can be carried out their just like any public area.
Some private BS going on for supposed security reasons like a few other places in London, but over all the security are now aware and will ask politely instead about stuff like tripod hazards, (under the cover of commercial licencing fulfilments, insurance coverage etc)...However that's the same for any commercial use of a public-highway, a film licence is needed! ..they just use it as a BS way to enforce something legal ish, when in effect there's nothing illegal in everyday tourist type photography.