Old queen opening supermarket had help (9)
I believe the answer is:
cooperate
'help' is the definition.
(I've seen this before)
'old queen opening supermarket had' is the wordplay.
'old queen' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'opening' is an insertion indicator (some letters open a gap in others).
'supermarket' becomes 'Co-op' (The Co-operative).
'had' becomes 'ate' ('have' can mean 'eat').
'coop'+'ate'='coopate'
'er' placed into 'coopate' is 'COOPERATE'.
(Other definitions for cooperate that I've seen before include "Work together on a common enterprise" , "work hand in glove" , "getting act together" , "fit in with others" , "Work to the same end" .)