Toffs landed in dock (7)
I believe the answer is:
quality
'toffs' is the definition.
(quality can informally mean upper-class people)
'landed in dock' is the wordplay.
'landed' becomes 'lit' (I've seen this in another clue).
'in' indicates putting letters inside.
'dock' becomes 'quay' (quay is a kind of dock).
'lit' going within 'quay' is 'QUALITY'.
(Other definitions for quality that I've seen before include "Standard or grade" , "Degree of excellence" , "Excellent" , "Timbre" , "General excellence" .)