Complex sentence: He became the BBC's chief political correspondent in 1999, and between 2002 and 2005 he worked for ITV News as political editor, but then returned to the BBC assuming the same role, which he has held since.
Split into simpler sentences: He became the BBC's chief political correspondent in 1999. Between 2002 and 2005 he worked for ITV News as political editor, but then returned to the BBC assuming the same role, which he has held since.