Although it's close to the MI5 building
Its MI6 not MI5 ! MI5 is on the north side of the river !
And if you've ever driven around that part of the world, you'll find the MI6 building is nestled between some of those ghastly residential new developments and some old buildings on the other side.... so its not exactly exposed.
There was some construction work going on to build yet another ghastly residential development..... so let's stop the MI6 conspiracy theories shall we ! Seems like the thing hit the construction crane, nothing more.