There is an article by Bryan Appleyard in the dead tree edition of today's Sunday Times Culture magazine, about the play and includes a brief interview with Joseph, who apparently is in the process of losing 2 stone in weight for the role.
"I have to look the part, as there does seem to be an implicit understanding in the play of how long he has been in these terrible places. There' is a kind of addiction to matyrdom in him that has quite a bit of glamour in it. It seems quite important to him that his name is known in the west."

 

The play, in this article, is also described as an inspired farce, where speeches are riddled with superb gags which have to be picked up in a hurry. 
"It feels like a kind of catch up game and thats kind of plausible. You are bombarded with wit, and you cant hang around for each one to land. You have to fly through."