In reply to DrJP:
Just been in an email conversation discussing this. The upshot is that Blatant Buttress looks like it is properly a no-go crag now - it was always pretty dodgy TBH.
Blackwell Halt, on the other hand, should be fine still as long as you don't use the approach in the BMC Peak Limestone North guide and instead use the one in the Rockfax:
From the Monsal Trail on the Chee Dale Upper Approach, head down towards the cafe/cycle hire. Cross the bridge and turn sharp left at the cottages and follow a small path along the edge of the river and past a pump house. This leads to a tunnel under the train tracks. On leaving the tunnel, cross the fence on the left and go up some hidden stone steps. From here a path leads up into the grassy field below the quarry.
I have marked the UKC logbook entry up accordingly - Chee Dale Upper
Alan
Post edited at 14:50