Former PM, having no answer, ruined (4)
I believe the answer is:
sunk
'ruined' is the definition.
(I know that ruined can be written as sunk)
'former pm having no answer' is the wordplay.
I cannot quite understand how this works, but
'no' could be 'n' (common abbreviation) and 'n' is located in the answer.
The remaining letters 'suk' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sunk that I've seen before include "ruined" , "Doomed - bored" , "Sent to bed" , "(Has) disappeared beneath the waves" , "Dropped; in a fix" .)