Inspector on his own inviting recruit without much success (15)

I believe the answer is:

disappointingly

'without much success' is the definition.
(with disappointment)

'inspector on his own inviting recruit' is the wordplay.
'inspector' becomes 'di' (abbreviation for Detective Inspector).
'on his own' becomes 'singly' (by oneself).
'inviting' indicates putting letters inside.
'recruit' becomes 'appoint' (recruit can mean to appoint someone).
'singly' placed around 'appoint' is 'sappointingly'.
'di'+'sappointingly'='DISAPPOINTINGLY'

I've seen this clue in The Times.

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