Critique - I don't think that is a BBC News set, but then again comedy shows have done very good mock ups before - it seems a waste of money given they could have just asked the Newsnight team to record it after an episode or on a Saturday when B sits idle.
Perhaps it was to satisfy the usual requirement that a spoof news bulletin must vary from the real thing.
Though that rule appears to have been relaxed. At one point it was either :
1. Real presenter on fake set
2. Fake presenter on real set
But you weren't allowed real presenter on real set with fake news.
However this was definitely relaxed a while ago (though maybe only in some situations). ISTR that Spooks getting Sky News to do all the 'fake news' for a series may have triggered a change of view.
The BBC have certainly allowed real presenters on real sets for a while now - subject to availability. There have been quite a few examples of note, the obvious (and already mentioned) Huw Edwards appearance on Skyfall, but Joanna Gosling appeared repeatedly in an international production in the mid-00s reading fake news in a real studio. So much show she featured in the trailer here :