Next week, Germany's best theatre company is coming to London for the first time. In the 50s and 60s it was obligatory for theatre fans and critics from all over Germany to make the pilgrimage to East Berlin to see each new production of Brecht's Berliner Ensemble. Now, just across the wall, Die Schaubuhne, a young and politically committed theatre co-operative, has by general international consensus replaced the Berliner Ensemble as the finest German company.