Tim Etchell's blog at the Guardian continues to be very good:
It's watching this small fraction of inspired improvisations (maybe 3% would be more accurate) that reminds me how lucky I am to work with performers who can do this – this very strange combination of tuning and turning, doing and waiting, acting and not acting, pretending, playing, inventing, insisting, listening and taking chances. It might be an odd thing for a sometime writer like me to say, but watching this kind of rehearsal, when the group is on a roll, and being lucky enough to nudge it into shape a bit, reconfirms so many of my doubts about the singularity of authorship that many plays demand. I really do prefer the making by doing, the group effort, its multiple directions and endless live negotiations. Even the cold of the bunker, and the ever-present threat of an eight-hour circular discussion, can't keep me away.