In reply to C Witter:
Sorry Chris, but I think this one is special. I've been climbing 50 years including a large number of outings on UK mountain cliffs and I don't think I've ever found a serious accident so waiting to happen. I've never reported loose blocks before and I have, of course, found many. This one is right where a climber (including me on Saturday) is likely inadvertently to place a hand while making the final easy moves. I touched it and was very lucky I didn't send it down directly onto my belayer. It's now even more precariously balanced than before.
Your reference to a "spate" of recent posts on here about loose blocks perhaps refers to the large block on The Fang at Gowther Crag. Perhaps also to the huge pinnacle on Shadrach. Both of these have been well dealt with following reporting but would have remained accidents waiting to happen unless someone had reported them.
Yes, you are right that trundling is generally to be frowned upon. Perhaps there might be parties climbing on Lliwedd in rotten weather though I think it's not very likely, especially midweek. I will, as I suggested, alert mountain rescue.
Martin