BBC2 I think. I've also tried to find all of the Barry Welsh shows. I have 2 on VHS but think I've lost one. They were the official compilation releases but I'm going to order them on DVD anyway.
I have the majority of the Absolutely cast's work including all of their own radio shows dating back to the early 80's and their productions under their Absolutely Productions company but there's still the few things eluding me.
Yes, Mac was definitely on main BBC2 - I had it on video (taped off telly, obvs) for years, until the tape fucked.
The entirety of Barry Welsh WAS on YouTube until as recently as last year - I watched the whole lot. Stupidly, though, I didn't rip them and they soon disappeared. I think a few of them are still knocking around on Vimeo and/or Daily Motion.
One that I'd like to find, that I've mentioned on CaB before, but sadly don't have many details beyond childhood memories - shown on BBC2 in the daytime in the mid 80s. Looked like it was made in the early 80s or late 70s. It was a spoof science show from one of the Scandinavian countries, and the comical narration was just directly translated into English. It was NOT a serious science show given comedy narration, the visuals were clearly comedy as well. Also, I am definitely not getting confused with Look Around You, as I remember seeing this when I was off school for a couple of weeks with mumps when I was 6 or 7. Don't remember much else, but there were two scientists/presenters featured - one with dark hair and clean shaven, the other blond with a 'tache. They both wore woolly jumpers.
Given my dad also found it funny, I'm pretty sure it wasn't a show specifically for kids (or, if it was, it also had the adults in mind, a la Horrible Histories), and I reckon it would probs be just as good seen now.
If anyone has any idea what I'm talking about, I would love to know more about it and see it again.