Group climbing at a very familiar crag, i(A) arrived and a top rope was set (by B) on a medium grade route (hvs /e1) several people had tried the route (C, D, E) and struggled to complete the crux moves, i was invited and had several attempts (x4?), unable to complete i was lowered off by my belayer (c) on lowering we looked up to find the ropes whole sheath worn thro and a large (3m?) part of white core showing, continued lowering me to floor, rope discontinued use.