Rudd's inconclusive investment in British currency showed discretion (8)
I believe the answer is:
prudence
'discretion' is the definition.
(I know that prudence is a type of discretion)
'rudd's inconclusive investment in british currency' is the wordplay.
'inconclusive' means to remove the last letter.
'investment in' is an insertion indicator.
'british currency' becomes 'pence' (I can't explain this - if you can you should give a lot more credence to this answer).
'rudd' with its final letter taken away is 'rud'.
'rud' inserted inside 'pence' is 'PRUDENCE'.
'showed' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for prudence that I've seen before include "Caution; common sense" , "The girl for wisdom and forethought" , "Caution, circumspection" , "Shrewdness in planning ahead" , "Quality of being cautious and sensible, and a girl's name" .)