Old PM is with artist opening shop (8)
I believe the answer is:
disraeli
'old pm' is the definition.
(Benjamin Disraeli, Victorian prime minister)
'is with artist opening shop' is the wordplay.
'with' is a charade indicator (letters next to each other).
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'opening' is an insertion indicator (some letters open a gap in others).
'shop' becomes 'deli' (deli is a kind of shop).
'is'+'ra'='isra'
'isra' going within 'deli' is 'DISRAELI'.
(Other definitions for disraeli that I've seen before include "Jane Austen novel" , "Ali dries out the old British prime minister" , "One of Queen Victoria's prime ministers" , "PM, bought Suez Canal" , "prime minister, in the past" .)