Theatre Archive Project
One more thought, if you expand out to include the US, the Harry Ransom Center at U. of Texas might be something to look at: http://www.hrc.utexas.edu/collections/performingarts/. They have performing arts materials, though I'm not sure to what extent. They are one of the big dogs in the world of lit archives though, so I'm guessing they could have a decent amount of performing arts materials as well.
Hi, Katie!
Oh, aren't they just the big dogs, though! Man, it's almost worth going to Texas just to see all the amazing things they have there. They are like the Yankees of the special collections world...when you have all the money, you get all the marbles (that is a mixed metaphor if I have ever heard one!).
I am sure you already found this, but just in case you didn't, the Harry Ransom Center and the University of Reading Library in the U.K. developed this "a database of copyright contacts for writers, artists, and prominent figures in other creative fields," which might be helpful for your section on literary archives and copyright.