[DTV]

Would BBC World News have devoted up to 4 hours of live, continuous coverage over to British politics from Westminster before March 2020?

Excepting general election night, no. More broadly, BBC World News very rarely took live coverage of any extended of these kinds of committee/news conference at all until fairly recently. It's certainly been mutating into more of a rolling news channel in the last few years (including slowing down to News channel pacing, which has in itself slowed down), but this is fairly without precedent and rather ridiculous.