That's interesting as the clip they always show on '90s documentaries is that of John Humphrys reporting on the 'Battle of Britpop'.
A quick jaunt through Genome points out that John Humphrys stopped reading the news in December 1986, before joining Today in January 1987, but then returned in the summer of 1989, primarily on the Six - presumably the period between Nicholas Witchell stopping and Peter Sissons joining - and from then on he made semi-regular appearances on all the bulletins for many years, perhaps unsurprisingly mostly in the summer while the regulars were away. His last appearance reading the news on Genome is in December 1998.
I remember when he was on The Frank Skinner Show, Frank showed clips of him closing the One O'Clock News on several occasions by putting his pen in his jacket pocket, then presenting him with a jacket with several dozen pens in the pocket.
As for Jill Dando, she's first billed in Genome on Breakfast Time in May 1988, which was the time they went from the presenters reading the news to the return of a proper newsreader. The first time she does the whole show is in the summer of 1989, but she progressed very quickly, presenting the Six for the first time not long after.
I’m still not a massive fan of the format - I think with interviews it can often be better if both presenters ‘share the load’, so to speak - but I can certainly see how it has merit.
I think generally, fixed bulletins can work well with one presenter, whereas rolling news (especially during the day) is often better with two.
I always like double-headed news presentation, I think it's a shame we don't have it on any bulletin at the moment because it seems a bit warmer. Of course, the high water mark of double-headed presentation was in 1985-86 when all three of the main BBC bulletins used it.