Stop aluminium coming in — that’s popular (9)
I believe the answer is:
prevalent
'popular' is the definition.
(thesaurus)
'stop aluminium coming in' is the wordplay.
'stop' becomes 'prevent' (I've seen this before).
'aluminium' becomes 'al' (chemical symbol).
'coming in' is an insertion indicator.
'prevent' placed around 'al' is 'PREVALENT'.
'that's' acts as a link.
(Other definitions for prevalent that I've seen before include "Ruling" , "powerful" , "Widespread - current" , "Common" , "Commonplace" .)