Of course "Blue Planet" was mastered in 50i (I already stated that) I meant for other 25 fps material that really was mastered at 24. I personally wouldn't do a 25->24 slow down because it is hard to figure out which method to use for each source even if you know what it was mastered in. Reclock after the fact works well for me too, though this would change if targeting non-PC playback. Happily, given the PDF you linked smok3, it looks like anything from the BBC, 2011 or newer at least, should be mastered at 50i. This is probably true for everything from the BBC before 2011 too but I don't know how to be sure.