Having rewatched bits of what I'd dozed through, I think I understand a bit more, though still not that much. At 1:04 in the second yt video, IO starts her presentation by explaining that the respondent's position is that BC's case was "an attempt to challenge the findings of facts made by the ET by dressing them up as points of law". This is important because this court of appeal is not supposed to be considering facts, I think - it's supposed to trust the ET to have determined those, and to be considering law only. At the ET, both sides seem to have been looking for "but for" causation plus "the mental element" in KM's complaint causing a detriment to AB. What that "mental element" needed to be, if anything, seems to be part of what BC was talking about, but I'm legally out of my depth here. It's related to the different requirements in the case where B's discrimination against C is direct vs indirect, and both were at issue at the original ET, so one would have to get that clear to understand fully what's going on here. As a matter of fact, the ET found
377. As for causing, in the “but for” sense it is true that if Kirrin Medcalf had not written, Maya Sikand’s report would have been limited to the original batch referred, which she would have dismissed without investigation. The email was the occasion of the report, no more. Was the letter an attempt to cause discrimination against the claimant? We concluded that it was no more than protest, with an appeal to a perceived ally in a ‘them and us’ debate.
but this seems to be in conflict with their also have accepted KM's evidence
369. Challenged on why he was not more specific about what he wanted, he said he had “had his advocacy hat on”, which we understand to mean that he was writing to protest about her views (stated to come from a member of Garden Court) and put the case for trangendered people. In other words, he wrote without any specific aim in mind except perhaps a public denial of association with her views.
He was, I think, denying that he wanted to get AB ejected from chambers, and the ET accepted that - but a public denial of association with her views would also have been a detriment, so the two passages above do not seem to be consistent. Whether that is fact or law is too deep for me...And if I understood correctly, BC was arguing that in fact it doesn't matter what KM's intentions were anyway, or indeed whether they were accomplished - it's enough, he argued, to read the complaint objectively and see that it is, in fact, most naturally read as an attempt to induce GCC to act against AB.
Looking forward to hearing lawyers' interpretations of all this at some point!