Complex sentence: Morrison became a thorn in the side of the Drury government by opposing its alliance with urban workers and the labour movement and was instead an advocate of non-partisan "group government", a position rejected by Drury.
Split into simpler sentences: Morrison became a thorn in the side of the Drury government on various levels. Morrison opposed the UFO's alliance with urban workers and the labour movement and was instead an advocate of non-partisan "group government", a position rejected by Drury.