To not want my boss to call me lazy because I can't make a course that starts at 8.15am?

[dilemma456]

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Yes your boss is a twat, for sure. But TBH honest I would not go running to HR just yet, in my experience this just creates extra stress for you and might unfortunately backfire. Do save emails etc, but given that this course is (presumably?) a one off, just get there late and let him know afterwards that you attended, I am just wary of you being angry (rightly so) and creating a big deal that might not be uneceesary???

good luck and hang on in there

I would email and ask him to reconsider his decision to pull you off the course as a result of your inability to get childcare for that particular time slot at such short notice. Make the point that you would only be x minutes late and that that time would be for coffee/chat as he well knows. That way if he says no then you have the whole episode in writing. File it for future reference as I suspect this won't be the last time this happens.

Good luck.

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good.
it's not fair of him to be such a twat be so unaccommodating (in both a legal and human way). especially when you have other problems that lie on top.

go to the course at the times you planned, as you said. also advise the course leaders that you are late because of childcare commitments and that the course time was changed at short notice.

and do tell HR, even if you think it's not a big issue now: the main reason for this is that if the course leaders then tell your boss that you arrived at 8:45 due to childcare commitments, he might tll HR that you were late on purpose and try to use it against you in the future.

YANBU and if he's been stupid enough to do this by e-mail then it's to your advantage: save, backup, forward to another e-mail account of yours, etc.
I agree you should keep it purely factual though - feelings do matter but are beside the point when it comes to discrimination law.