In reply to Oliver Hill:
What are people doing about it now? I remember that you could climb quite safely, even doing it as a roped lead, by the 'Boulder Bridge Route' (2b). You back and foot up the wide chasm behind IB to a break, then sidle along to the 'boulder' (here placing a huge thread runner) then traverse very pleasantly at about 2a/b across the top of Wailing Wall round Crowborough Arete, thence to top very easily. A good long route in its own right, actually. I'm fairly sure I've reversed it too quite easily.
The undergraded Isolated Buttress Climb ("4c") – surely 5a, even by SS standards? – is a very scary solo (IMHO) and would be much/even harder in descent.
PS. 'In the mountains', Boulder Bridge Route would probably be given something like [Ogwen] 'Hard Very Difficult' or 'Mild Severe'
Post edited at 23:53