The Guardian article is misleading to the point of dishonesty. The episode that isn't being broadcast was not intended to be broadcast because it isn't part of the Wild Isles series. It's a companion documentary commissioned by the RSPB and the WWF.

And for all the good both these charities do, the BBC should not be broadcasting programs made by what are, in effect, political lobbying organizations (and I say that as someone who agrees with their aims).

Look at the last paragraph in the article, where they've put the real reason it isn't being broadcast.

Lineker compared the Home Secretary to the Nazis. He's entitled to his personal opinions, but he's a very prominent and massively over-paid BBC employee, so he should know better than to air his views on Twitter.