Not right when there’s sauce for Cockney to go after sandwiches (6)
I believe the answer is:
unjust
'there's sauce for cockney to go after sandwiches' is the definition.
I can't judge whether this defines the answer.
'not right' is the wordplay.
'not' becomes 'un' (I've seen this in other clues).
'right' becomes 'just' ('just' can be similar in meaning to 'right'**).
'un'+'just'='UNJUST'
'when' acts as a link.
(Other definitions for unjust that I've seen before include "Biased" , "Inequitable" , "Not fair or equitable" , "Unfair" , "Partisan - not fair" .)