Most ancient member of upper chamber breaking ties (8)
I believe the answer is:
earliest
'most ancient' is the definition.
(I've seen this in another clue)
'member of upper chamber breaking ties' is the wordplay.
'member of upper chamber' becomes 'earl' (member of the House of Lords).
'breaking' is an anagram indicator (back).
'ties' is an anagram of 'iest'.
'earl'+'iest'='EARLIEST'
(Other definitions for earliest that I've seen before include "Original or most previous" , "Furthest back in time" , "Very first in a sterile manner" , "Ateliers (anag.)" , "The first to arrive - to get the worm?" .)