Do Not Adjust Your Set was a children's comedy airing in the U.K. from 1967-69. Most notably, it was the show that first assembled most (4/6) of the Monty Python team. Here's my favorite clip from the show - Eric Idle singing Captain Fantastic, with all of the regulars (including Terry Jones, Michael Palin, David Jason, Neil Innes, and Denise Coffey) clowning around in the background. ("Captain Fantastic" was the name of the most popular recurring sketch on the show.)
It's a very catchy song - much in the style of pop music at the time. And yes, that's the Bonzo Dog Doo-Dah Band backing up Idle.