Those old enough to remember the days when the BBC showed a great deal of dance material which covered important developments in dance in the twentieth century rather than being restricted to films about Margot may not realise that John Drummond was responsible for much of the output which made the BBC seem such a dance friendly institution.
In the late 1960's John Drummond made a two part documentary about Diaghilev.. Part one Diaghilev; The Years Abroad is available on BBC i-Player. It includes contributions from Karsavina,Sokolovam Rambert,Nabokov and Beaumont .I have no idea whether it is there in perpetuity or whether it is only available for a limited time.but it is well worth watching.
Unfortunately part two The Yeras in Exile is not available.