Writer Julian Mitchell and actor Kenneth Branagh remember the struggle to mount a risky anti-establishment play, and how Rupert Everett did his best to spice it upIn 1979, when Mrs Thatcher stood up in the Commons and announced that the third man in the Burgess and Maclean spy case was Anthony Blunt, lots of people wrote articles and books saying how easy it must have been for these men to go over to Russia. But thei…