I think the voice gives the game away which is a good thing. People will realise it is not really her Maj but it will also educate people on deepfake videos
Sadly I think there's plenty of thickoes out there who will believe it, in the same way that many believe some of the crap they read on Twitter. Have a guess at how many Americans believe every word that Trump tweets for example (no, I've no idea of the number either, but I'll wager it needs several noughts at the end of it!)
As far as Channel 4 broadcasting it, the kindest thing I can say about it is 'unnecessary'.