Complex sentence: During the Common Market referendum Varley advocated a'No' vote but was not prominent in the campaign; immediately after it, Wilson swapped jobs between him and Benn, being promoted to Secretary of State for Industry.
Split into simpler sentences: During the Common Market referendum Varley advocated a'No' vote but was not prominent in the campaign. Immediately afterwards Wilson swapped Varley's and Benn's posts, so that Varley was effectively promoted to Secretary of State for Industry.