Complex sentence: At that time he was a member of the Militant Tendency, which was carrying out an entry tactic inside the Labour Party, and Mutton was responsible for getting the then Leader of Council Peter Lister deselected and replacing him.
Split into simpler sentences: At that time he was a member of the Militant tendency, which was carrying out an entry tactic inside the Labour Party. John Mutton was responsible for getting the then Leader of Council Peter Lister deselected and replacing him.