I don't want to rain on everyone;'s parade but I have seen it pointed out on twitter that the 6th episode wasn't part of the planned series, which was always gong to be in 5 parts. The sixth episode was funded separately by charities and filmed independently. The BBC only ever planned to put it on IPlayer.
I do not know the truth, or otherwise of this. Conflicting screen shots were posted during the twitter exchange.
Read the full guardian article, that shows that episode 6 was definitely “ cut”