Complex sentence: On 1 September 2008 the Labour Party published its list for the 2008 general election and ranked Chauvel at number 27, up 17 places on his 2005 ranking--amongst the 8 most significant advancements when comparing the 2005 and 2008 party lists.
Split into simpler sentences: On 1 September, the Labour Party published its list for the 2008 general election. This was amongst the 8 most significant advancements when comparing the 2005 and 2008 party lists.