Swap Shop.
Our region in ITV land - Tyne Tees- didn't carry Tiswas until its later series before it ended, so missed a lot of it. Wasn't it local to Brum for its first few years?.
There is some debate about who got a first with 70's Saturday morning kids telly with 3-hour long shows punctuated by cartoons etc. I think Tiswas started out a a series of links between other programmes, so wasn't really an entity in itself until later. Still, found it just too silly, with distracting OTT slapstick.
I watched Swap Shop from its inception but vaguely recall an earlier Saturday morning show which was 'introduced' by a computer & featured a weekly serial which was illustrated and was about an environmental catastrophe causing the world to freeze. I think it featured the cult newspaper strip character 'Garth'. The show also featured a weekly time-travel visit to the past to see different dinosaurs...that's all I can remember!!.
Of course, even way back...HR Pufnstuff??