Complex sentence: In 2005 Powergen was ranked by Energywatch one of the UK's worst suppliers, by the end of 2006 they were ranked the UK's second best-a position they have held on to since this date.
Split into simpler sentences: In 2005 Powergen was ranked by Energywatch as one of the UK's worst suppliers. However, by the end of 2006 they were ranked the UK's second best-a position which they have held on to since this date.