Complex sentence: An opinion poll conducted by the centre-left think tank Compass found in March 2009 that Mandelson was less disliked by party members than deputy party leader Harriet Harman, very unusual as Mandelson "historically has been unpopular among Labour members".
Split into simpler sentences: An opinion poll conducted by the centre-left think tank Compass found in March 2009 that Mandelson was less disliked by party members than deputy party leader Harriet Harman. This was felt to be unusual as Mandelson "historically has been unpopular among Labour members".