The sitting member won't have such a reputation! (8)
I believe the answer is:
standing
'reputation' is the definition.
(one's standing is one's reputation or status)
'the sitting member won't have such a' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
'a' could be 'an' and 'an' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for standing that I've seen before include "Being a candidate - status" , "Status, reputation" , "Upright" , "Social or financial status" , "Buying a round on one's feet" .)