Year in party elected to take on most of the complex situation (9)
I believe the answer is:
labyrinth
'the complex situation' is the definition.
'year in party elected to take on most' is the wordplay.
'year' becomes 'yr' (abbreviation).
'in' indicates putting letters inside.
'party' becomes 'lab' (abbreviation for Labour).
'elected' becomes 'in'.
'to take on most' becomes 'th' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lab'+'in'='labin'
'yr' placed inside 'labin' is 'labyrin'.
'labyrin'+'th'='LABYRINTH'
'of' is the link.
(Other definitions for labyrinth that I've seen before include "Maze, tangled network" , "part of hearing" , "perplexing route" , "Passages in cutting" , "Complex network of passages" .)