I forgot about Matt Berry's Television Themes album and am here to report, three years late, that you may now get it (along with the others he has since released). The selection is a 1970s dinner party of memories, diced and served in aspic, from naff gameshow Blankety Blank to apocalyptic current affairs show World In Action, popular classics such as Doctor Who and Top of the Pops, but also liminal bullseyes such as The Open University and various TV station idents. The inclusion of the deeply weird Picture Box theme (i.e. Jacques Lasry's Manége) is a particularly hauntological delight.
Embedded above is his rendition of the Rainbow theme. Rainbow is classic UK children's TV, cheap and cheerful, with that faintly cursed aura about it that mid-late 20th century UK children's TV often has. If Berry's cover isn't intrinsically amusing yet charming in its sincere attention to detail and quality execution, you are perhaps not a British Gen-X/millennial nostalgia junkie.
