Distinguished member of upper house possibly gathering army (7)
I believe the answer is:
notable
'distinguished member of upper' is the definition.
'notable' can be an answer for 'distinguished' (thesaurus). I'm not sure about the 'member of upper' bit.
'house possibly gathering army' is the wordplay.
'house possibly' becomes 'noble' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'gathering' is an insertion indicator.
'army' becomes 'ta' (abbreviation for Territorial Army).
'noble' enclosing 'ta' is 'NOTABLE'.
Can you help me to learn more?
(Other definitions for notable that I've seen before include "Star" , "Famous or memorable" , "Worth remembering" , "Great" , "Eminent" .)