Complex sentence: Following that election, Letwin remained Chancellor of the Duchy of Lancaster and Cameron also appointed him as a full member of the new Conservative government's Cabinet with responsibility for overall charge and oversight of the Cabinet Office.
Split into simpler sentences: Following that election, Letwin remained Chancellor of the Duchy of Lancaster and Cameron also appointed him as a full member of the new Conservative government's Cabinet. He was given responsibility for overall charge and oversight of the Cabinet Office.