He had a key qualification in the premiership (5)
I believe the answer is:
major
'key qualification in the premiership' is the definition.
'major' can be an answer for 'key' (thesaurus). I'm unsure of the 'qualification in the premiership' bit.
'he had a' is the wordplay.
I cannot really see how this works, but
'he' could be 'jo' and 'jo' is found within the answer.
'a' is present in the answer.
The remaining letters 'mr' 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 major that I've seen before include "1 down's predecessor" , "Military rank" , "Of greater importance or stature" , "grave" , "John --, prime minister" .)