Update - the Yuanmingyuan documentary has now been released in an English language version on Youtube. Please note, the documentary covers the whole history of Yuanmingyuan and not just the destruction of it as stated in the title of the post.
Find it here
I've updated my essay about the making of the film and some of the questions surrounding the second Opium War here - in particular I've included references to some of the currently available historical materials that can be found on the internet. It might be of improved interest now to anyone interested in that period of history.