It's important to remember that Nolan and Thompson could do what they did, not just because Northern Ireland has its own peculiar political culture which means BBCNI takes a slightly different approach to impartiality, but also because BBC bosses in London see BBCNI as a regional backwater and don't pay attention to it.
This is one of the many revelations in Andrew Lownie's book on Andrew and Fergie - despite the books and TV dramas giving you the impression that Newsnight did a thorough investigation into Andrew's affairs, it really didn't. It was a Panorama team in NI led by Laura Burns, who's since left the BBC, who did all the digging and came up with the evidence and the list of questions.
The Palace was simultaneously negotiating with Newsnight for a soft soap interview with Andrew, with the result that the Panorama doc was pulled and at 72 hours notice their material was handed over to Newsnight.
With no disrespect to Emily Maitlis, the main reason why it didn't turn out to be a soft soap interview is because ex-Prince Andrew is a very stupid and arrogant man who told a string of outrageous lies, and Emily was smart enough to let him keep on digging a hole for himself.
BBCNI really never gets the credit it's due.