Rainbow was a real children's television show that appeared on British television in the 1970s and 1980s.
However, I don't think this episode was written for the kiddies.
The sketch opens with Zippy peeling a banana...
Zippy: "One skin, two skin, three skin, four.... "
George: "Zippy, where is Bungle?"
Zippy: "I think Geoffrey is trying to get him up"
We see a view of the door and hear Bungle moaning from behind it.
Bungle: "Geoffrey, I can't get it in"
Geoffrey: "You managed it last night"
Bungle: "I know, let's try it round the other way around. Ooooooh, I've got it in"