Complex sentence: Two years later, he became the Conservative spokesman for social services, in 1999 the deputy leader of the Conservative group, in 2003 the group leader, and in 2006 the Council leader.
Split into simpler sentences: Two years later, he became the Conservative spokesman on social services. Then, in 1999, he became the deputy leader of the Conservative group, and in 2003 the group leader, and in 2006 the Council leader.