Small catch when man working on the house accepts direct debit (7)
I believe the answer is:
tiddler
'small catch' is the definition.
(small fish)
'man working on the house accepts direct debit' is the wordplay.
'man working on the house' becomes 'tiler' (a tiler works on a roof).
'accepts' means one lot of letters goes inside another.
'direct debit' becomes 'DD' (abbreviation).
'tiler' going around 'dd' is 'TIDDLER'.
'when' acts as a link.
(Other definitions for tiddler that I've seen before include "Little chap" , "Small fry" , "Small thing" , "A small fish children try to catch" , "Minnow" .)