Very lucky gent finally occupying working toilet (4,3)
I believe the answer is:
only too
'very' is the definition.
(I've seen this before)
'lucky gent finally occupying working toilet' is the wordplay.
'finally' says to take the final letters.
'occupying' indicates putting letters inside (inserted letters occupy or enter the word).
'working' becomes 'on' (on can mean working or activated).
'toilet' becomes 'loo' (loo can informally mean a toilet).
The last letters of 'lucky gent' are 'yt'.
'on'+'loo'='onloo'
'yt' going inside 'onloo' is 'ONLY TOO'.
(Another definition for only too that I've seen is " Regrettably".)