As Iam points out, KS was a key worker, so would, of course, be attending work. My work has staff development training all the time. People attend during working hours, and some of it is mandatory.
I'm waiting to see the outcome of any prosecution before leaping to judgement, but legalities aside, what I'm seeing is the usual knee-jerk reactions, language such as 'trotting out' (have we had 'bleating' yet?) and personal comments about Starmer's voice. Surely if you are leader of the opposition, aware that your voice is holding you back , and you know that an election is in the offing you would take steps to correct that? His team will be aware of the sort of comments we get on here, and the even worse ones on other SM, so taking steps sounds perfectly valid to me, but of course the 'balanced' view is that if Labour do something it is all kinds of wrong, but when the Tories do it it is excusable.
Margaret Thatcher had voice coaching, incidentally.
The question, I think, is around whether the classes were 'essential' given the vague and ever-changing diktats of the time. I couldn't possibly say, but I expect that an inquiry (should there be a need for one - I'd be surprised if this wasn't all throughly vetted at the time) will determine this, as the people involved will have actual facts, rather than gossip and speculation, at their disposal.
Re Zoom - my (admittedly limited) knowledge of voice coaching suggests that the coach needs to touch the chest and abdomen to teach breathing techniques, and that there is other physical contact - the voice is part of the body and can't be accessed remotely.
I can think of quite a number of murderous dictators who scored very highly on that front.