The mystery of the yellow 'planks' is solved. The mysterious yellow shelves which stick out like this have been identified by googling the contents of this photo.
The basic concept of the Xena Cantilever Crane is a simple crane that feeds DL Access platforms and relives [sic] tower cranes.That's the first time I've usd [sic].
small cranes, made especially for high rise buildings. These cranes props in between floors, and have got telescoping boom and hoisting facilities only. The crane is controlled from a single joystick, located on the crane.So it would seem that the main tower cranes are used for hoisting materials to the top of the tower - they can do that as they extend beyond its apex. But the Alexa cranes are used for hoisting materials to already completed floors. Not particularly exiting, but not what I expected to be the answer either.
It's not the only new way of getting materials in. At the rear is a loading bay, at the front is a new vehicle entrance, there are new steps (closely guarded by security guards I think, judging by the hut), and even a cherry-picker style machine in case all other cranes fail. It's a hive of activity!!!
I am of course yet to see anybody doing anything though as I visit at the weekend. I do, however, have some holiday to take before April so that may change.