Wulfhound, looking at it there are actually islands in the middle of the road at all 3 branches of the junction:
The south circular is already very wide at that junction, widening from one to two lanes east bound, and is nearly as wide on the westbound side. Looks to me like there would be plenty of scope there for building a larger island for pedestrians without grabbing privately owned land. And to use the land in front of the grove would mean relocating some or all those street lamps and/or the mobile phone mast / telpehone exchanges that are there.