Complex sentence: By 1986, under their supervision, "Spitting Image" had become popular, producing a number one song on the UK Singles Chart ("The Chicken Song "), but Grant and Naylor subsequently left to create"Red Dwarf" for BBC2.
Split into simpler sentences: By 1986, under their supervision, "Spitting Image" had become popular, producing a number one song on the UK Singles Chart ("The Chicken Song "). However, Grant and Naylor subsequently left to create"Red Dwarf" for BBC2.