The fence got put up sometime last year. Vert sensible addition as that section of the platform is regularly overcrowded so having an open platform face was an accident waiting to happen.
Unfortunately, as can be seen from your photo and the other one earlier in the thread, they seem to have chosen to add just about the most ugly construction possible, which faces you every time you enter the station.
It also significantly narrows the walking routes to and from the platforms, increasing congestion, especially when the signaller for whatever reason decides to switch an incoming train between platform 1 and platform 4 (or 1 and 7) at the last moment, which is a fairly common occurrence.
I'm not aware of anyone actually falling off here in the 25+ years I've been regularly using the station, and I struggle to see why this has been added, other than to be seen to be doing something for the sake of it. And if they really felt they had to be seen to be doing something about the non-extant problem, couldn't they at least have done something a little more aesthetically acceptable?