They're forever blown at West Ham playing Blues to win two billion (7)
I believe the answer is:
bubbles
'they're forever blown at west ham' is the definition.
(West Ham United anthem I'm Forever Blowing Bubbles)
'playing blues to win two billion' is the wordplay.
'playing' indicates an anagram.
'to win' is an insertion indicator.
'two' shows that letters should be duplicated.
'billion' becomes 'b'.
'blues' anagrammed gives 'bules'.
'b' duplicated is 'bb'.
'bules' placed around 'bb' is 'BUBBLES'.
(Other definitions for bubbles that I've seen before include "Little balls of soap and water" , "is very vivacious" , "Fizzes" , "Michael Jackson's monkey" , "Old song: 'I'm forever blowing .......'" .)